Fix build on Mac OS X

For some users -stack_size,0x4000 does not work,
so revert for now.

osX 10.6.8
gcc version 4.7.3 (MacPorts gcc47 4.7.3_2)

g++: error: unrecognized command line option '-stack_size,0x4000'
make[2]: *** [stockfish] Error 1
make[1]: *** [gcc-profile-make] Error 2
make: *** [profile-build] Error 2

No functional change.