Add parallelism support to gcov for MinGW platforms

Add parallelism support to gcov for MinGW platforms

If you attempt a profiled bootstrap on the MinGW platforms with -jN, N > 1,
it miserably fails because of profile mismatches all over the place, the
reason being that gcov has no support for parallelism on these platforms.

libgcc/
	* libgcov.h: For the target, define GCOV_LOCKED_WITH_LOCKING
	if __MSVCRT__ and, for the host, define it if HOST_HAS_LK_LOCK.
	* libgcov-driver.c: Add directives if GCOV_LOCKED_WITH_LOCKING.
gcc/
	* configure.ac: Check for the presence of sys/locking.h header and
	for whether _LK_LOCK is supported by _locking.
	* configure: Regenerate.
	* config.in: Likewise.
	* gcov-io.h: Define GCOV_LOCKED_WITH_LOCKING if HOST_HAS_LK_LOCK.
	* gcov-io.c (gcov_open): Add support for GCOV_LOCKED_WITH_LOCKING.
	* system.h: Include <sys/locking.h> if HAVE_SYS_LOCKING_H.