[gimp] configure: run AX_PROG_CC_FOR_BUILD before AM_PROG_CC_C_O.

[Jehan Pagès <jehanp src gnome org>]

commit 3618df0999461397fc51ab90dcb7cc1807504c86
Author: Jehan <jehan girinstud io>
Date:   Mon Jun 13 01:47:19 2016 +0200

    configure: run AX_PROG_CC_FOR_BUILD before AM_PROG_CC_C_O.
    
    It was working fine for me, but someone had the error:
    error: AC_PROG_CC cannot be called after AM_PROG_CC_C_O
    /usr/share/aclocal/ax_prog_cc_for_build.m4:38: AX_PROG_CC_FOR_BUILD is expanded
    from...
    I can indeed see that AX_PROG_CC_FOR_BUILD code runs AC_PROG_CC again.
    So let's make sure this is run before AM_PROG_CC_C_O.
    Thanks to Francesco Riosa for reporting the bug.

 configure.ac |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index ce00b8a..2ea32c6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -220,6 +220,7 @@ AS_IF([test "x$0" != "x./configure"], [
 
 # Determine a C compiler to use
 AC_PROG_CC
+AX_PROG_CC_FOR_BUILD
 AM_PROG_CC_C_O
 
 # Determine a C++ compiler to use
@@ -2075,8 +2076,6 @@ if test "x$enable_vector_icons" = "xyes"; then
 fi
 
 if test "x$enable_vector_icons" = "xyes"; then
-  AX_PROG_CC_FOR_BUILD
-
   # We must not use $PKG_CONFIG nor PKG_CHECK_* macros because we need
   # to make sure we use the native pkg-config (in case we cross-compile).
   if pkg-config --atleast-version=glib_required_version glib-2.0 &&