amd64: make bcmp in libc just call memcmp

Preferably bcmp would just alias memcmp but there is build magic which
makes this problematic.

Reviewed by:	jhb
Differential Revision:		https://reviews.freebsd.org/D28846

lib/libc/amd64/string/Makefile.inc

@@ -1,7 +1,6 @@
 # $FreeBSD$
 
 MDSRCS+= \
-	bcmp.S \
 	memcmp.S \
 	memcpy.S \
 	memmove.S \

lib/libc/amd64/string/bcmp.c

@@ -0,0 +1,16 @@
+/*-
+ * Written by Mateusz Guzik <mjg@freebsd.org>
+ * Public domain.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <string.h>
+
+int
+bcmp(const void *b1, const void *b2, size_t len)
+{
+
+	return (memcmp(b1, b2, len));
+}