Disable aliasing when building with Clang

When building with new versions of Clang we encounter some issues. Work
around them by adding -fno-strict-aliasing when we detect Clang.

https://code.google.com/p/webm/issues/detail?id=603

Change-Id: I8e945a18a7215bcc627e7a1ee110078413259cc7

configure

@@ -608,7 +608,12 @@ process_toolchain() {
         check_add_cflags -Wuninitialized
         check_add_cflags -Wunused-variable
         case ${CC} in
-          *clang*) ;;
+          *clang*)
+              # libvpx and/or clang have issues with aliasing:
+              # https://code.google.com/p/webm/issues/detail?id=603
+              # work around them until they are fixed
+              check_add_cflags -fno-strict-aliasing
+          ;;
           *) check_add_cflags -Wunused-but-set-variable ;;
         esac
         enabled extra_warnings || check_add_cflags -Wno-unused-function