Use ifunc to dynamically dispatch libc routines for x86

Test: run bionic unit test in aosp_cf_x86_phone emulator
Change-Id: Ib0c0de37cd38d24bfce2dfbe35b8fd8edff004af
diff --git a/libc/arch-x86/silvermont/string/sse4-wmemcmp-slm.S b/libc/arch-x86/silvermont/string/sse4-wmemcmp-slm.S
index 2c350bb..2bf92f5 100755
--- a/libc/arch-x86/silvermont/string/sse4-wmemcmp-slm.S
+++ b/libc/arch-x86/silvermont/string/sse4-wmemcmp-slm.S
@@ -29,5 +29,5 @@
 */
 
 #define USE_AS_WMEMCMP
-#define MEMCMP wmemcmp
+#define MEMCMP wmemcmp_sse4
 #include "sse4-memcmp-slm.S"