force to load MD5 related functions.
emulate OSAtomicAdd32 and OSAtomicAdd32.

See Also:
OSAtomicAdd32 and OSAtomicAdd64 manual:
https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man3/OSAtomicAdd64.3.html

GCC online document:
5.44 Built-in functions for atomic memory access.
http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Atomic-Builtins.html
Fix pthread_mutex_lock not to halt.

Since PTHREAD_MUTEX_INITIALIZER is different between Linux and Mac,
ld-mac halted when the program calls pthread_mutex_lock with
mutex initialized with PTHREAD_MUTEX_INITIALIZER.

To avoid the problem, I have inserted a hook to pthread_mutex_lock
to be initialized with Linux mutex lock.
Fake implementation of Block.

If we need real implementation, we might need to consider to import:
http://compiler-rt.llvm.org/
Remove -lcrypto

I believe we don't need this anymore thanks to
c38b5896d1c07f500b01ba6a2eb96fbd8e32aad6