When building on MacOS:
* greadlink instead of readlink
* gsed instead of sed
* $TMPDIR instead of a hardcoded /tmp
* apply a macos-specific patch
* additional option to GCC
Additionally, don't rely on the system 'isl' stuff; always have binutils
build its own.
The forum post also says that bumping mpfr 3.1.x to 4.1.x, and mpc
from 1.0.x to 1.2.x is needed, but I do not want to do that due to the
possibility of unknown codegen changes.
Change-Id: I18084d392fa927318cc2a1183da7eb2ffa0d5884
