x86: Remove the unused __x86_prefetchw

Since

commit c867597bff
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Wed Jun 8 13:57:50 2016 -0700

    X86-64: Remove previous default/SSE2/AVX2 memcpy/memmove

removed the only usage of __x86_prefetchw, we can remove the unused
__x86_prefetchw.

sysdeps/i386/Makefile

@@ -13,10 +13,6 @@ ifeq ($(subdir),math)
 CFLAGS-e_gamma_r.c += -DMATH_SET_BOTH_ROUNDING_MODES
 endif
 
-ifeq ($(subdir),string)
-sysdep_routines += cacheinfo
-endif
-
 ifeq ($(subdir),gmon)
 sysdep_routines += i386-mcount
 endif

sysdeps/i386/cacheinfo.c

@@ -1,3 +0,0 @@
-#define DISABLE_PREFETCHW
-
-#include <sysdeps/x86/cacheinfo.c>

sysdeps/x86/Makefile

@@ -14,6 +14,10 @@ gen-as-const-headers += jmp_buf-ssp.sym
 sysdep_routines += __longjmp_cancel
 endif
 
+ifeq ($(subdir),string)
+sysdep_routines += cacheinfo
+endif
+
 ifneq ($(enable-cet),no)
 ifeq ($(subdir),elf)
 sysdep-dl-routines += dl-cet

sysdeps/x86/cacheinfo.c

@@ -536,11 +536,6 @@ long int __x86_rep_movsb_threshold attribute_hidden = 2048;
 /* Threshold to use Enhanced REP STOSB.  */
 long int __x86_rep_stosb_threshold attribute_hidden = 2048;
 
-#ifndef DISABLE_PREFETCHW
-/* PREFETCHW support flag for use in memory and string routines.  */
-int __x86_prefetchw attribute_hidden;
-#endif
-
 
 static void
 get_common_cache_info (long int *shared_ptr, unsigned int *threads_ptr,
@@ -831,17 +826,6 @@ init_cacheinfo (void)
 	  /* Account for exclusive L2 and L3 caches.  */
 	  shared += core;
 	}
-
-#ifndef DISABLE_PREFETCHW
-      if (max_cpuid_ex >= 0x80000001)
-	{
-	  unsigned int eax;
-	  __cpuid (0x80000001, eax, ebx, ecx, edx);
-	  /*  PREFETCHW     || 3DNow!  */
-	  if ((ecx & 0x100) || (edx & 0x80000000))
-	    __x86_prefetchw = -1;
-	}
-#endif
     }
 
   if (cpu_features->data_cache_size != 0)

sysdeps/x86_64/Makefile

@@ -18,7 +18,7 @@ tests += tst-mallocalign1
 endif
 
 ifeq ($(subdir),string)
-sysdep_routines += cacheinfo strcasecmp_l-nonascii strncase_l-nonascii
+sysdep_routines += strcasecmp_l-nonascii strncase_l-nonascii
 gen-as-const-headers += locale-defines.sym
 endif