Naming convention for AVX

Signed-off-by: Timothy B. Terriberry <tterribe@xiph.org>

celt/x86/x86cpu.h

@@ -46,6 +46,12 @@
 #  define MAY_HAVE_SSE4_1(name) name ## _c
 # endif
 
+# if defined(OPUS_X86_MAY_HAVE_AVX)
+#  define MAY_HAVE_AVX(name) name ## _avx
+# else
+#  define MAY_HAVE_AVX(name) name ## _c
+# endif
+
 # if defined(OPUS_HAVE_RTCD)
 int opus_select_arch(void);
 # endif