Fix implicit declaration of GC_setup_mark_lock.

boehm_gc/misc.c:
	Include pthread_support.h for GC_setup_mark_lock,
	a Mercury-specific addition.
Enable thread-local allocation and parallel marking on more platforms.

The changes to the platforms that I am unable to test are based on the
boehm_gc/configure script.  If that script allows the features to be
enabled then I assume that the features are usable.

configure.ac:
	Enable parallel marking on Solaris (untested by me).

	Enable on Cygwin (untested by me).

	Enable on MinGW32 (tested).

	Enable on MinGW-w64 (tested with winpthreads, which requires some
	other changes).

	Enable on Darwin (tested by Julien).