Somehow the entire plugin infrastructure went wholly untested until now.
The only plugins available for use in testing are the examples, so plugin tests
will only be run if CLANG_BUILD_EXAMPLES is enabled in the build.
(The examples should really be enabled by default, not just to aid testing but
also to prevent bitrot in some key user-facing code. I'll propose that
shortly.)
Requires supporting changes in LLVM r198746.
llvm-svn: 198747