[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: 52ce677
See: 136f778
Closes: llvm#60394

Reviewed By: MaskRay

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

Author: thesamesam

compiler-rt/test/lit.common.cfg.py

@@ -733,3 +733,10 @@ def is_windows_lto_supported():
       sh_quote(get_ios_commands_dir())
     ))
   )
+
+# It is not realistically possible to account for all options that could
+# possibly be present in system and user configuration files, so disable
+# default configs for the test runs. In particular, anything hardening
+# related is likely to cause issues with sanitizer tests, because it may
+# preempt something we're looking to trap (e.g. FORTIFY_SOURCE vs our ASAN).
+config.environment["CLANG_NO_DEFAULT_CONFIG"] = "1"