autoconf: Enable missing-prototypes errors when available.

After the removal of the dri driver link test, this should help avoid
the original problem that it was designed to catch: The warning about
a missing prototype due to typoing a function name scrolling by in the
Mesa build spew, and you not noticing until you try to run an
application and it falls back to swrast.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

diff --git a/configure.ac b/configure.ac
index df9f880..d42a529 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -176,7 +176,20 @@ esac
 
 dnl Add flags for gcc and g++
 if test "x$GCC" = xyes; then
-    CFLAGS="$CFLAGS -Wall -Wmissing-prototypes -std=c99"
+    CFLAGS="$CFLAGS -Wall -std=c99"
+
+    # Enable -Werror=implicit-function-declaration and
+    # -Werror=missing-prototypes, if available, or otherwise, just
+    # -Wmissing-prototypes.  This is particularly useful to avoid
+    # generating a loadable driver module that has undefined symbols.
+    save_CFLAGS="$CFLAGS"
+    AC_MSG_CHECKING([whether $CC supports -Werror=missing-prototypes])
+    CFLAGS="$CFLAGS -Werror=implicit-function-declaration"
+    CFLAGS="$CFLAGS -Werror=missing-prototypes"
+    AC_LINK_IFELSE([AC_LANG_PROGRAM()],
+                  AC_MSG_RESULT([yes]),
+                  [CFLAGS="$save_CFLAGS -Wmissing-prototypes";
+                   AC_MSG_RESULT([no])]);
 
     # Enable -fvisibility=hidden if using a gcc that supports it
     save_CFLAGS="$CFLAGS"