libc: x86: Use SSE2 or SSSE3 optimized routines when possible.

This patch uses the new hardware feature macros for x86 to define
various compile-time macros used to make the C library use
SSE2 and/or SSSE3 optimized memory functions for target CPUs
that support these features.

Note that previously, we relied on the macros being defined by
build/core/combo/, but this is no longer the

Change-Id: Ieae5ff5284c0c839bc920953fb6b91d2f2633afc
diff --git a/libc/ b/libc/
index caeab8c..5d851df 100644
--- a/libc/
+++ b/libc/
@@ -513,7 +513,12 @@
 else # !arm
   ifeq ($(TARGET_ARCH),x86)
     libc_crt_target_cflags :=
-    # TARGET_GLOBAL_CFLAGS from build/core/combo/ sets all required flags.
+    ifeq ($(ARCH_X86_HAVE_SSE2),true)
+        libc_crt_target_cflags += -DUSE_SSE2=1
+    endif
+    ifeq ($(ARCH_X86_HAVE_SSSE3),true)
+        libc_crt_target_cflags += -DUSE_SSSE3=1
+    endif
   endif # x86
 endif # !arm