tcc failed to run with bounds checking enabled because the functions
rt_wait_sem, rt_post_sem and _rt_error where defined twice.
This is solved by making them weak in tccrun.c
Also a nested lock was present when setting TCC_BOUNDS_PRINT_CALLS=1
This is solved in lib/bt-exe.c by moving lock/unlock code.
Also added a testcase in tests/Makefile to test tcc with bounds
checking enabled.