Built SDL2_image and _mixer static

libsdl2_mixer/external/flac-1.3.2/m4/add_cxxflags.m4

@@ -0,0 +1,19 @@
+dnl @synopsis XIPH_ADD_CXXFLAGS
+dnl
+dnl Add the given option to CXXFLAGS, if it doesn't break the compiler
+
+AC_DEFUN([XIPH_ADD_CXXFLAGS],
+[AC_MSG_CHECKING([if $CXX accepts $1])
+	AC_LANG_ASSERT([C++])
+	ac_add_cxxflags__old_cxxflags="$CXXFLAGS"
+	CXXFLAGS="$1"
+	AC_TRY_LINK([
+			#include <cstdio>
+			],
+		[puts("Hello, World!"); return 0;],
+		AC_MSG_RESULT([yes])
+			CXXFLAGS="$ac_add_cxxflags__old_cxxflags $1",
+		AC_MSG_RESULT([no])
+			CXXFLAGS="$ac_add_cxxflags__old_cxxflags"
+		)
+])# XIPH_ADD_CXXFLAGS