[test] Adding config initialization to lit tests in clang-tools-extra

[juliehockett]

Summary

Adding the config initialization (the footer) to clang-tools-extra so that tests that use REQUIRES, UNSUPPORTED, and XFAIL based on platform or target triple work properly.

[lebedev.ri]

Nice catch!
I wonder how many more test/lit.site.cfg.in are silently partially non-functional because they don't have that substitution...

I also have an idea why it might not have worked for you - are you building clang-tools-extra repo separately manually, not as part of the whole llvm build?

[lebedev.ri]

As per https://github.com/llvm-project/llvm-project-20170507/search?utf8=%E2%9C%93&q=LIT_SITE_CFG_IN_FOOTER&type=
this substitution already exists in most of the repos.
I don't see why it should not be in *all* top-level test/lit.site.cfg.in's.
(if it should not be, why is it in clang's, even though llvm's already has it?)

Though, here (c-t-e is built as part of the llvm), REQUIRES: windows works as expected.

test/lit.site.cfg.in

try:
     config.clang_tools_dir = config.clang_tools_dir % lit_config.params
     config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
     config.llvm_libs_dir = config.llvm_libs_dir % lit_config.params
 except KeyError:
     e = sys.exc_info()[1]
     key, = e.args
     lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key,key))
 
+@LIT_SITE_CFG_IN_FOOTER@
+
 # Let the main config do the real work.
 lit_config.load_config(config, "@CLANG_TOOLS_SOURCE_DIR@/test/lit.cfg")