Merge bitcoin/bitcoin#24792: Update libsecp256k1 subtree to current master

404c53062bb80853d5967187bdb7b5f7e749de7f key: use secp256k1_schnorrsig_sign32 over deprecated secp256k1_schnorrsig_sign (fanquake)
ee30bf7c01922938bcf861a57cdf2249edb36256 build: remove some no-longer-needed var unexporting from configure (fanquake)
2656629767b098d17245a66e0bfa4c2c62f20d0c build: remove --enable-experimental from libsecp256k1 configure (fanquake)
d960d4fd3a767cf5695bed96c5f329056f77d0da build: fix MSVC build after subtree update (dhruv)
afb7a6fe06a33956ef43429d31f5934448f6e671 Squashed 'src/secp256k1/' changes from 0559fc6e41..8746600eec (fanquake)

Pull request description:

  The motivation for this bump is some small build cleanups, including [dropping the `--enable-experimental`](https://github.com/bitcoin-core/secp256k1/commit/80cf4eea5fa0162350614c08f2252a07f9d7804b) flag from the libsecp configure  invocation, as well as some [now-redundant](https://github.com/bitcoin-core/secp256k1/pull/1090) `pkg-config` variable exporting from our own configure. We also get the benefit of a slightly more efficient libsecp configure due to https://github.com/bitcoin-core/secp256k1/pull/1088.

  This also includes a change in our code to migrate from using the [now deprecated](https://github.com/bitcoin-core/secp256k1/commit/99e6568fc6ea2768f5355eb4617283086f756931) `secp256k1_schnorrsig_sign` to `secp256k1_schnorrsig_sign32`.

  Guix Build (on x86_64):
  ```bash
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  250d47ae299d8385d5590518fa2adaabde76e2566fd27e12bf36b62663d13e13  guix-build-404c53062bb8/output/aarch64-linux-gnu/bitcoin-404c53062bb8-aarch64-linux-gnu-debug.tar.gz
  48d610dc6f5169f925f782571dac2f082695f89008beadad4adef4c1b583a612  guix-build-404c53062bb8/output/aarch64-linux-gnu/bitcoin-404c53062bb8-aarch64-linux-gnu.tar.gz
  8f04ee26e4079719e3935bd0e4287cc11a2a16875bf01e2a63d67492a1fa5367  guix-build-404c53062bb8/output/arm-linux-gnueabihf/SHA256SUMS.part
  7d7d7fcfb032bda92e53abd8d608257f0ef17b1e3e52a1414260b896786fb2dc  guix-build-404c53062bb8/output/arm-linux-gnueabihf/bitcoin-404c53062bb8-arm-linux-gnueabihf-debug.tar.gz
  30bae2ff3d044f4e39f992a68f6b296b7be2aea350bca4a0415c739a32c20bd9  guix-build-404c53062bb8/output/arm-linux-gnueabihf/bitcoin-404c53062bb8-arm-linux-gnueabihf.tar.gz
  5f550fb0b950250eeffce3480ec6403530b0880570a5860ef6c32a3e92eac92f  guix-build-404c53062bb8/output/arm64-apple-darwin/SHA256SUMS.part
  c10664d13aeec8c860bf72be833c738973ae18e4d28cdf08b2f9bee960ebff1d  guix-build-404c53062bb8/output/arm64-apple-darwin/bitcoin-404c53062bb8-arm64-apple-darwin-unsigned.dmg
  becab75b11cf4ca6f559f8eef835f3574629f6eb932ac716ed4f8c044a85831f  guix-build-404c53062bb8/output/arm64-apple-darwin/bitcoin-404c53062bb8-arm64-apple-darwin-unsigned.tar.gz
  bc86433652fe3552f6a13088191364ae7514c9fe3a244da86a6db096bb4922fc  guix-build-404c53062bb8/output/arm64-apple-darwin/bitcoin-404c53062bb8-arm64-apple-darwin.tar.gz
  1f585cb9a1356343df4b2726ecfe2598c9903304afb047c047c2cef318555dd3  guix-build-404c53062bb8/output/dist-archive/bitcoin-404c53062bb8.tar.gz
  9ede534ba2c6cecb550473eead195627327e826ebb0118e23d60ab482d40e241  guix-build-404c53062bb8/output/powerpc64-linux-gnu/SHA256SUMS.part
  77ddb7d7d639b1dd4508468a8ef27e45b35c8b2f8624584a70e6b64798a4ea7a  guix-build-404c53062bb8/output/powerpc64-linux-gnu/bitcoin-404c53062bb8-powerpc64-linux-gnu-debug.tar.gz
  36178c1f1c12942ff05275daa3570f8b45419ee8d9f391d750afb405219986f0  guix-build-404c53062bb8/output/powerpc64-linux-gnu/bitcoin-404c53062bb8-powerpc64-linux-gnu.tar.gz
  8a15a4da7a9a5e00c49d9aeedf3c6fc666c0d230be1369eac7caf4571d5905e0  guix-build-404c53062bb8/output/powerpc64le-linux-gnu/SHA256SUMS.part
  400c58113f2d07c87e03c8528b292c6aca808a2bccae4b041cad3a26a05b6aad  guix-build-404c53062bb8/output/powerpc64le-linux-gnu/bitcoin-404c53062bb8-powerpc64le-linux-gnu-debug.tar.gz
  3b9f9d8614ac3a27416e53354b2b0a64d364f91493e9d0f41583a6f492546824  guix-build-404c53062bb8/output/powerpc64le-linux-gnu/bitcoin-404c53062bb8-powerpc64le-linux-gnu.tar.gz
  98506b23ee08ad8af958f816da2e4518d661e88d5c6308de1f5e3b2fc787b86c  guix-build-404c53062bb8/output/riscv64-linux-gnu/SHA256SUMS.part
  c701a7b77cea4fdc2588b511f1b2c71b89c83bfba19fdb2ac113a5a4b14ac392  guix-build-404c53062bb8/output/riscv64-linux-gnu/bitcoin-404c53062bb8-riscv64-linux-gnu-debug.tar.gz
  34d58e6392cd58b3c76e30cd8600c0dbefba7e9c6d5df78c3ef23e81c4e4d26a  guix-build-404c53062bb8/output/riscv64-linux-gnu/bitcoin-404c53062bb8-riscv64-linux-gnu.tar.gz
  92fa30e9c6d81dd1e1514b65d3e1abe68ded897237cd99f66aa760d445109c04  guix-build-404c53062bb8/output/x86_64-apple-darwin/SHA256SUMS.part
  bee180b02f178ae9980ef159f65913a71cbd037c4aff5f2906af5f174a677da3  guix-build-404c53062bb8/output/x86_64-apple-darwin/bitcoin-404c53062bb8-x86_64-apple-darwin-unsigned.dmg
  ad7d18d779ab7a7944817d1f368d0a6bdd174bf1211b0f90180c8ccf04ec4062  guix-build-404c53062bb8/output/x86_64-apple-darwin/bitcoin-404c53062bb8-x86_64-apple-darwin-unsigned.tar.gz
  7489d1d5d48ad95cf58bb11b5fdeccadac6fa758784fb498529fca2330abe069  guix-build-404c53062bb8/output/x86_64-apple-darwin/bitcoin-404c53062bb8-x86_64-apple-darwin.tar.gz
  74660fb0ebce2a08b03980a57bffcad62e078dc967a74d2395660ff51c019640  guix-build-404c53062bb8/output/x86_64-linux-gnu/SHA256SUMS.part
  cd377fa6b46276c2f8a32e199e6f9adf6aa67315688656709d6dc0744d54a837  guix-build-404c53062bb8/output/x86_64-linux-gnu/bitcoin-404c53062bb8-x86_64-linux-gnu-debug.tar.gz
  919c521950369d8ad46db2d15b00abb488abfb080d157a41b2db429122a428ed  guix-build-404c53062bb8/output/x86_64-linux-gnu/bitcoin-404c53062bb8-x86_64-linux-gnu.tar.gz
  2debca995d432965a8786b6ff74aed42e9e2f1cb0fecbe2d9fc5b850c192fcff  guix-build-404c53062bb8/output/x86_64-w64-mingw32/SHA256SUMS.part
  e33169f684fb031ec18ed39812617d3eb263257f6c7564b8f4c974ad05fe672c  guix-build-404c53062bb8/output/x86_64-w64-mingw32/bitcoin-404c53062bb8-win64-debug.zip
  029d0a4180cb908d517fcf689dcf46d42fbf383e11dc609711617066ae039ab0  guix-build-404c53062bb8/output/x86_64-w64-mingw32/bitcoin-404c53062bb8-win64-setup-unsigned.exe
  7e349c688cac66436562c4805f420b0536db5a3b3abf54d0e8c7752f59874a5c  guix-build-404c53062bb8/output/x86_64-w64-mingw32/bitcoin-404c53062bb8-win64-unsigned.tar.gz
  1bff98e82e95c93d6060227408502f5e2d8597d526b912cb6dc0a90ae3094a8f  guix-build-404c53062bb8/output/x86_64-w64-mingw32/bitcoin-404c53062bb8-win64.zip
  ```

ACKs for top commit:
  laanwj:
    Code review ACK 404c53062bb80853d5967187bdb7b5f7e749de7f, I checked the changes to our tree thoroughly but didn't review all upstream secp256k1 changes in detail.
  gruve-p:
    ACK https://github.com/bitcoin/bitcoin/pull/24792/commits/404c53062bb80853d5967187bdb7b5f7e749de7f
  real-or-random:
    utACK 404c53062bb80853d5967187bdb7b5f7e749de7f I reviewed the diff to Core, I'm with updating to libsecp256k1 master, but I haven't verified that the libsecp256k1 tree here has been updated correctly

Tree-SHA512: e6a6db93ea60ed500df5065178784a915da94adfa7bd45fdbd7b19d701154987ff38c1df7f318119e6c2cb98e28e1ea2eb725bef93d4088403e14537ebffb032

1 files changed, 121 insertions, 0 deletions

diff --git a/src/secp256k1/examples/EXAMPLES_COPYING b/src/secp256k1/examples/EXAMPLES_COPYING
new file mode 100644
index 0000000000..0e259d42c9
--- /dev/null
+++ b/src/secp256k1/examples/EXAMPLES_COPYING
@@ -0,0 +1,121 @@
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