[PATCH] [compiler-rt][builtins] CTest to execute builtins testsuite

[Sumanth Gundapaneni]

This builds the unit tests along with the library.
We want to build the unit tests when invoked with "check-builtins". Isn't it?

I am writing the lit cfg files for test/builtins and will upload it when I am done testing it.

http://reviews.llvm.org/D4251