Switch check_clang_tidy to argparse and add a -resource-dir argument.

-resource-dir can be used to inject non-standard resource dirs via the
lit site config.

llvm-svn: 251021
diff --git a/clang-tools-extra/test/clang-tidy/modernize-loop-convert-lowercase.cpp b/clang-tools-extra/test/clang-tidy/modernize-loop-convert-lowercase.cpp
index e38006e..a8081db 100644
--- a/clang-tools-extra/test/clang-tidy/modernize-loop-convert-lowercase.cpp
+++ b/clang-tools-extra/test/clang-tidy/modernize-loop-convert-lowercase.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s modernize-loop-convert %t \
+// RUN: %check_clang_tidy %s modernize-loop-convert %t -- \
 // RUN:   -config="{CheckOptions: [{key: modernize-loop-convert.NamingStyle, value: 'lower_case'}]}" \
 // RUN:   -- -std=c++11 -I %S/Inputs/modernize-loop-convert