This fixes an issue with mono where JIT compiled code would
near-call wrapped libraries, but fail because the difference
between PC and the call address did not fit into an imm32.

This was fixed by replacing posix_memalign with my_mmap and
providing the MAP_32BIT flag.

Fixes ptitSeb#131

FreeBridge used free to clean up the pointer allocated by
my_mmap, which is incorrect and lead to a crash upon code
that exited gracefully.

The free was replaced with my_munmap.

This adds a declaration of my_mmap and my_munmap to
src/tools/bridge.c in order to avoid a
-Wimplicit-function-declaration warning when compiling.

This should probably be moved to a header file in the
future.