[PowerPC] Remove FreeBSD test in mm-malloc.c due to cross-compilation limitation

Fix failures on powerpc BE buildbots
https://lab.llvm.org/buildbot/#/builders/93/builds/6031
https://lab.llvm.org/buildbot/#/builders/100/builds/10836
https://lab.llvm.org/buildbot/#/builders/52/builds/12719

GitOrigin-RevId: b0784d1d14246e5d662172e9af6e85776b81fdf0
1 file changed