add -Wmissing-prototypes

clang treats -Wmissing-declarations differently than gcc. This
provides similar coverage for clang.

Fix vpx_clear_system_state() warning on 32bit builds:
  note: this declaration is not a prototype; add 'void' to make it a
  prototype for a zero-parameter function

Change-Id: I5a424bc38d47c0a3dc751d65c1efea5733907785

1 files changed, 2 insertions, 0 deletions

diff --git a/configure b/configure
index b5096723b..2174544c3 100755
--- a/configure
+++ b/configure
@@ -627,6 +627,8 @@ process_toolchain() {
           add_cflags_only -Wframe-larger-than=52000
         check_cflags -Wmissing-declarations && \
           add_cflags_only -Wmissing-declarations
+        check_cflags -Wmissing-prototypes && \
+          add_cflags_only -Wmissing-prototypes
         if enabled mips || [ -z "${INLINE}" ]; then
           enabled extra_warnings || check_add_cflags -Wno-unused-function
         fi