PrintAsObjC Test: Ignore poison directories warnings for C

Author: xymus

test/PrintAsObjC/lit.local.cfg

@@ -14,7 +14,7 @@ config.substitutions.insert(0, ('%check-in-clang-c',
   '%%clang -fsyntax-only -x c-header -std=c99 -fmodules '
   '-fmodules-validate-system-headers '
   '-Weverything -Werror -Wno-unused-macros -Wno-incomplete-module '
-  '-Wno-auto-import '
+  '-Wno-auto-import -Wno-poison-system-directories '
   '-F %%clang-importer-sdk-path/frameworks '
   '-I %%clang-include-dir '
   '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )