Remove useless x86 fallbacks.

The NDK ABI requires that you support SSE2, and the build system won't let you
build with ARCH_X86_HAVE_SSE2 set to false. So let's stop pretending this
constant is actually a variable, and let's remove the corresponding dead code.

Also, the USE_SSE2 and USE_SSE3 macros are unused, so let's not bother
setting them.

Change-Id: I40b501d998530d22518ce1c4d14575513a8125bb
diff --git a/libc/arch-x86/x86.mk b/libc/arch-x86/x86.mk
index ada5d69..395f0d4 100644
--- a/libc/arch-x86/x86.mk
+++ b/libc/arch-x86/x86.mk
@@ -50,7 +50,6 @@
 	upstream-freebsd/lib/libc/string/wmemcmp.c
 endif
 
-ifeq ($(ARCH_X86_HAVE_SSE2),true)
 _LIBC_ARCH_COMMON_SRC_FILES += \
 	arch-x86/string/sse2-memset-atom.S \
 	arch-x86/string/sse2-bzero-atom.S \
@@ -64,23 +63,7 @@
 	arch-x86/string/sse2-wcschr-atom.S \
 	arch-x86/string/sse2-wcsrchr-atom.S \
 	arch-x86/string/sse2-wcslen-atom.S \
-	arch-x86/string/sse2-wcscmp-atom.S
-else
-_LIBC_ARCH_COMMON_SRC_FILES += \
-	arch-x86/string/memset.S \
-	arch-x86/string/strlen.S \
-	arch-x86/string/bzero.S \
-	bionic/memrchr.c \
-	bionic/memchr.c \
-	bionic/strchr.cpp \
-	string/strrchr.c \
-	string/index.c \
-	bionic/strnlen.c \
-	upstream-freebsd/lib/libc/string/wcschr.c \
-	upstream-freebsd/lib/libc/string/wcsrchr.c \
-	upstream-freebsd/lib/libc/string/wcslen.c \
-	upstream-freebsd/lib/libc/string/wcscmp.c
-endif
+	arch-x86/string/sse2-wcscmp-atom.S \
 
 _LIBC_ARCH_STATIC_SRC_FILES := \
     bionic/dl_iterate_phdr_static.c \