Cygwin: x86_64: add wmemset assembler entry point

So far, wmemset used the C implemantation from newlib.  Let's use
the optimized assembler code instead.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/Makefile.am

@@ -56,7 +56,8 @@ TEST_LIB_NAME=libcygwin0.a
 if TARGET_X86_64
 TARGET_FILES= \
 	x86_64/memcpy.s \
-	x86_64/memset.s
+	x86_64/memset.s \
+	x86_64/mcountFunc.S
 endif
 
 LIB_FILES= \
@@ -357,8 +358,7 @@ MALLOC_FILES= \
 GMON_FILES= \
 	gmon.c \
 	mcount.c \
-	profil.c \
-	mcountFunc.S
+	profil.c
 
 GENERATED_FILES= \
 	sigfe.s

winsup/cygwin/x86_64/memset.s

@@ -67,3 +67,11 @@ L1:     rep
 	movq	16(%rsp),%rdi
 	ret
 	.seh_endproc
+
+	.globl  wmemset
+	.seh_proc wmemset
+wmemset:
+	.seh_endprologue
+	shlq	$1,%r8		/* cnt * sizeof (wchar_t) */
+	jmp	memset
+	.seh_endproc