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/atom/string/ssse3-memcmp-atom.S b/libc/arch-x86/atom/string/ssse3-memcmp-atom.S
index 0387084..be2c4f6 100644
--- a/libc/arch-x86/atom/string/ssse3-memcmp-atom.S
+++ b/libc/arch-x86/atom/string/ssse3-memcmp-atom.S
@@ -76,7 +76,7 @@
 #endif
 
 #ifndef MEMCMP
-# define MEMCMP	memcmp
+# define MEMCMP	memcmp_atom
 #endif
 
 #define CFI_PUSH(REG)	\