It seems that if codesigning the test executables with the
`com.apple.private.security.no-sandbox` entitlement then the simulator refuses
to launch them and every test fails with `Process launch failed: process exited
with status -1 (no such process.)`.
This patch checks if we're trying to run the test suite on the simulator and
then avoids signing the executable with `no-sandbox`.
Reviewed By: JDevlieghere
Differential Revision: https://reviews.llvm.org/D89052
Instead of a new method for each variable any subclass might want to
set, have a method getExtraMakeArgs that each subclass can use to return
whatever extra Make arguments it wants.
As per Pavel's suggestion in D85539.
