boehm_gc: Fix declration of setup_mark_lock()

These patches have been applied to upstream boehm_gc by Ivan Maidanski.
We're applying them here as we're tracking their fixes for the TSX lock
elision bug.

boehm_gc/pthread_support.c:
    Rename GC_setup_mark_lock() to setup_mark_lock() and make it static.
    Add static declration of setup_mark_lock();
    Call setup_mark_lock() while setting up parallel marking.

boehm_gc/include/private/pthread_support.h:
    Remove declaration of GC_setup_mark_lock();

boehm_gc/misc.c:
    Remove call to GC_setup_mark_lock();
boehm_gc: Enable the TSX bug workaround on x86

Jan Alexander Steffens made this change to upstream boehm_gc.

boehm_gc/include/private/gcconfig.h:
    As above.