[compiler-rt] Disable default config files for tests

Without this, if hardening measures like FORTIFY_SOURCE are are in
/etc/clang/*.cfg, many sanitizer tests will die before the sanitizer
can trap the problem being tested, because e.g. the _chk variants
of common functions will abort first.

This gets the number of failing tests down from 42->3 for me (and the
remaining 3 are unrelated).

See: 52ce6776
See: 136f7780
Closes: https://github.com/llvm/llvm-project/issues/60394

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D143322