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-strcat-atom.S b/libc/arch-x86/atom/string/ssse3-strcat-atom.S
index d9b6129..8d8e89d 100644
--- a/libc/arch-x86/atom/string/ssse3-strcat-atom.S
+++ b/libc/arch-x86/atom/string/ssse3-strcat-atom.S
@@ -87,7 +87,7 @@
 #define POP(REG)	popl REG; CFI_POP (REG)
 
 #ifndef STRCAT
-# define STRCAT	strcat
+# define STRCAT	strcat_ssse3
 #endif
 
 #define PARMS	4
@@ -617,4 +617,4 @@
 	RETURN1
 
 #endif
-END (STRCAT)
+END (STRCAT_ssse3)