[gimp] Bug 787222 - Can't convert from 16 bit to 16 bit floating point.

[Jehan Pagès <jehanp src gnome org>]

commit 9b4382614be46468c3fbe384e7ffc73c9cb2bb43
Author: Jehan <jehan girinstud io>
Date:   Sat Sep 9 23:21:42 2017 +0200

    Bug 787222 - Can't convert from 16 bit to 16 bit floating point.
    
    This comes from a bug in GCC itself.
    Comparing with GCC's revision dates (bug introduced in revision 250312
    in 18th of July 2017), this bug apparently affects only GCC 7.2.
    Let's just add a configure warning so that builders are made aware of
    the issue when they use this compiler.
    See also: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82108

 configure.ac |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 4f4aa1d..dcff8d8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -530,6 +530,16 @@ if test "x$os_win32" = xyes; then
   fi
 fi
 
+if test "x$GCC" = xyes; then
+  gcc_version=`$CC -v 2>&1|grep 'gcc version'|sed -e 's/.*gcc version \([[0-9.]]\+\)[[^0-9.]].*/\1/'`
+  if test "x$gcc_version" = "x7.2.0" ; then
+    warning_gcc="
+WARNING: GCC 7.2.0 has a serious bug affecting GEGL/GIMP. We advise
+         against using this version of the compiler (previous and
+         further versions are fine).
+         See https://bugzilla.gnome.org/show_bug.cgi?id=787222";
+  fi
+fi
 
 AC_HEADER_STDC
 AC_HEADER_SYS_WAIT
@@ -2698,7 +2708,7 @@ Optional Modules:
 Tests:
   Use xvfb-run         $have_xvfb_run
   Test appdata         $have_appstream_util
-$have_recommended_xgettext$have_recommended_fontconfig$have_recommended_gtk$warning_vector_icons_windows$warning_glib_networking"
+$have_recommended_xgettext$have_recommended_fontconfig$have_recommended_gtk$warning_vector_icons_windows$warning_glib_networking$warning_gcc"
 
 if test "x$required_deps" = "x"; then
   AC_OUTPUT