when disabling -Werror, still use -Wall

mpeg2dec/configure.in

@@ -23,6 +23,10 @@ elif test x"$GCC" = x"yes"; then
     dnl GCC-specific flags
     dnl -Wall -Werror moved to the end to not disturb the configure script
 
+    dnl -Wall
+    OPT_CFLAGS="$CFLAGS -Wall"
+    AC_TRY_CFLAGS([$OPT_CFLAGS],[CFLAGS=$OPT_CFLAGS])
+
     dnl -O3
     changequote(<<,>>)
     OPT_CFLAGS=`echo "$CFLAGS"|sed "s/-O[0-9]*//g"`
@@ -111,7 +115,7 @@ AC_ARG_ENABLE([warnings],
     [  --disable-warnings      do not treat warnings as errors])
 if test x"$enable_warnings" != x"no" -a x"$GCC" = x"yes"; then
     dnl compiler warnings
-    OPT_CFLAGS="$CFLAGS -Wall -Werror"
+    OPT_CFLAGS="$CFLAGS -Werror"
     AC_TRY_CFLAGS([$OPT_CFLAGS],[CFLAGS=$OPT_CFLAGS])
 elif test x"$TENDRA" = x"yes"; then
     dnl TenDRA portability checking compiler