configure: check $CC available before verifying host CPU

When executing 'configure' in a fresh QEMU clone, in a fresh
OS install running in a ppc64le host, this is the error
shown:

-----

../configure --enable-trace-backend=simple --enable-debug
    --target-list=ppc64-softmmu

ERROR: Unsupported CPU = ppc64le, try --enable-tcg-interpreter

-----

This isn't true, ppc64le host CPU is supported. This happens because,
in a fresh install, we don't have a C compiler to autodetect
the $cpu variable to "ppc64".

This patch moves the CC available check up a bit, just before verifying
the host CPU. This ensures that we bail out with a $CC not available
error instead of unsupported CPU (the host CPU detection without
the compiler wouldn't work properly anyway). It also allows --help to
keep working without a C compiler. With this patch, in the same ppc64le
host without gcc:

$ ../configure --enable-trace-backend=simple --enable-debug
    --target-list=ppc64-softmmu

ERROR: "cc" either does not exist or does not work

$ ../configure --help

Usage: configure [options]
Options: [defaults in brackets after descriptions]

Standard options:
  --help                   print this message
  --prefix=PREFIX          install in PREFIX [/usr/local]
  --interp-prefix=PREFIX   where to find shared libraries, etc.
(...)

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

1 files changed, 14 insertions, 11 deletions

diff --git a/configure b/configure
index 0c6e7572db..9c8aa5a98b 100755
--- a/configure
+++ b/configure
@@ -1582,6 +1582,20 @@ fi
 # Suppress writing compiled files
 python="$python -B"
 
+# Check that the C compiler works. Doing this here before testing
+# the host CPU ensures that we had a valid CC to autodetect the
+# $cpu var (and we should bail right here if that's not the case).
+# It also allows the help message to be printed without a CC.
+write_c_skeleton;
+if compile_object ; then
+  : C compiler works ok
+else
+    error_exit "\"$cc\" either does not exist or does not work"
+fi
+if ! compile_prog ; then
+    error_exit "\"$cc\" cannot build an executable (is your linker broken?)"
+fi
+
 # Now we have handled --enable-tcg-interpreter and know we're not just
 # printing the help message, bail out if the host CPU isn't supported.
 if test "$ARCH" = "unknown"; then
@@ -1603,17 +1617,6 @@ if test -z "$werror" ; then
     fi
 fi
 
-# check that the C compiler works.
-write_c_skeleton;
-if compile_object ; then
-  : C compiler works ok
-else
-    error_exit "\"$cc\" either does not exist or does not work"
-fi
-if ! compile_prog ; then
-    error_exit "\"$cc\" cannot build an executable (is your linker broken?)"
-fi
-
 if test "$bogus_os" = "yes"; then
     # Now that we know that we're not printing the help and that
     # the compiler works (so the results of the check_defines we used