Fixed Emscripten build.

include/bx/float4_t.h

@@ -15,7 +15,7 @@
 #	include "float4_sse.h"
 #elif defined(__ARM_NEON__) && !BX_COMPILER_CLANG
 #	include "float4_neon.h"
-#elif BX_COMPILER_CLANG
+#elif BX_COMPILER_CLANG && !BX_PLATFORM_EMSCRIPTEN && __has_extension(attribute_ext_vector_type)
 #	include "float4_langext.h"
 #else
 #	ifndef BX_FLOAT4_WARN_REFERENCE_IMPL