Base bcopy on memmove rather than memcpy.

POSIX defined bcopy to handle overlapping memory akin to memmove and
bionic appears to have always done so.

Change-Id: I2599113411e3532913270ba1c1b49e35cbc5f106

libc/bionic/ndk_cruft.cpp

@@ -247,7 +247,7 @@ sighandler_t bsd_signal(int signum, sighandler_t handler) {
 // This was removed from POSIX 2008.
 #undef bcopy
 void bcopy(const void* src, void* dst, size_t n) {
-  memcpy(dst, src, n);
+  memmove(dst, src, n);
 }
 #else
 // x86 has an assembler implementation.