[PATCH v2 2/4] configure: Enforce gnu99 C language standard

[Daniel Kiper]

Commit d5a32255d (misc: Make grub_strtol() "end" pointers have safer
const qualifiers) introduced "restrict" keyword into some functions
definitions. This keyword was introduced in C99 standard. However, some
compilers by default may use C89 or something different. This behavior
leads to the breakage during builds when c89 or gnu89 is in force. So,
let's enforce gnu99 C language standard for all compilers. This way
a bit random build issue will be fixed and the GRUB source will be
build consistently regardless of type and version of the compiler.

It was decided to use gnu99 C language standard because it fixes the
issue mentioned above and also provides some useful extensions which are
used here and there in the GRUB source. Potentially we can use gnu11 too.
However, this may reduce pool of older compilers which can be used to
build the GRUB. So, let's live with gnu99 until we do not discover that
we strongly require a feature from newer C standard.

Signed-off-by: Daniel Kiper <address@hidden>
---
v2 - suggestions/fixes:
   - unconditionally enforce gnu99 C language standard
     (suggested by Leif Lindholm).
---
 configure.ac | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/configure.ac b/configure.ac
index b2576b013..fc74ee800 100644
--- a/configure.ac
+++ b/configure.ac
@@ -80,6 +80,10 @@ if test "x$TARGET_CFLAGS" = x; then
   TARGET_CFLAGS=-Os
 fi
 
+BUILD_CFLAGS="-std=gnu99 $BUILD_CFLAGS"
+HOST_CFLAGS="-std=gnu99 $HOST_CFLAGS"
+TARGET_CFLAGS="-std=gnu99 $TARGET_CFLAGS"
+
 # Default HOST_CPPFLAGS
 HOST_CPPFLAGS="$HOST_CPPFLAGS -Wall -W"
 HOST_CPPFLAGS="$HOST_CPPFLAGS -DGRUB_UTIL=1"
-- 
2.11.0