Summary: This patch adds gtest-like matchers and `EXPECT|ASSERT_THAT` macros. It also adds matchers `Succeeds` and `Fails` and has examples using these in test/src/signal/sigaddset_test.cpp.
Reviewers: sivachandra, gchatelet, PaulkaToast
Reviewed By: sivachandra, PaulkaToast
Subscribers: mgorny, MaskRay, tschuett, libc-commits
Differential Revision: https://reviews.llvm.org/D75487
Alex Brachet