The test precision_type.pass.cpp was a duplicate of precision.pass.cpp,
so it is removed. atomic_flag_test.pass.cpp was a duplicate of
atomic_flag_test_and_set.pass.cpp, so instead I wrote a proper
test for it. Those duplicate tests were detected with
find libcxx ! -empty -type f -exec md5sum {} + | sort | uniq -w32 -dD
C++98 and C++03 are effectively aliases as far as Clang is concerned.
As such, allowing both std=c++98 and std=c++03 as Lit parameters is
just slightly confusing, but provides no value. It's similar to allowing
both std=c++17 and std=c++1z, which we don't do.
This was discovered because we had an internal bot that ran the test
suite under both c++98 AND c++03 -- one of which is redundant.
Differential Revision: https://reviews.llvm.org/D80926