configure: Enable -Wvla if available.

[Thomas Faber]

A large number of fixes for MSVC build/C89 compatibility regularly
relate to variable-length arrays. GCC can warn about their use, so
enabling this warning can help prevent new issues of this type from
being added.

Yesterday's (well, today's) patches should have eliminated all current
occurrences of this warning, Wine builds with -Werror for me.
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From d492cbc46958e7deae4aa238e563a967c93fc2ea Mon Sep 17 00:00:00 2001
From: Thomas Faber <thomas.faber at reactos.org>
Date: Tue, 25 Mar 2014 07:50:30 +0100
Subject: configure: Enable -Wvla if available.

---
 configure    | 25 +++++++++++++++++++++++++
 configure.ac |  1 +
 2 files changed, 26 insertions(+)

diff --git a/configure b/configure
index 4d03970..6d8e85a 100755
--- a/configure
+++ b/configure
@@ -13695,6 +13695,31 @@ $as_echo "$ac_cv_cflags__Wunused_but_set_parameter" >&6; }
 if test "x$ac_cv_cflags__Wunused_but_set_parameter" = xyes; then :
   EXTRACFLAGS="$EXTRACFLAGS -Wunused-but-set-parameter"
 fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports -Wvla" >&5
+$as_echo_n "checking whether the compiler supports -Wvla... " >&6; }
+if ${ac_cv_cflags__Wvla+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_wine_try_cflags_saved=$CFLAGS
+CFLAGS="$CFLAGS -Wvla"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+int main(int argc, char **argv) { return 0; }
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_cflags__Wvla=yes
+else
+  ac_cv_cflags__Wvla=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+CFLAGS=$ac_wine_try_cflags_saved
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_cflags__Wvla" >&5
+$as_echo "$ac_cv_cflags__Wvla" >&6; }
+if test "x$ac_cv_cflags__Wvla" = xyes; then :
+  EXTRACFLAGS="$EXTRACFLAGS -Wvla"
+fi
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports -Wwrite-strings" >&5
 $as_echo_n "checking whether the compiler supports -Wwrite-strings... " >&6; }
 if ${ac_cv_cflags__Wwrite_strings+:} false; then :
diff --git a/configure.ac b/configure.ac
index 97874c4..2b56c7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1780,6 +1780,7 @@ then
   WINE_TRY_CFLAGS([-Wstrict-prototypes])
   WINE_TRY_CFLAGS([-Wtype-limits])
   WINE_TRY_CFLAGS([-Wunused-but-set-parameter])
+  WINE_TRY_CFLAGS([-Wvla])
   WINE_TRY_CFLAGS([-Wwrite-strings])
 
   dnl Check for noisy string.h
-- 
1.8.3.2