[libcxx] [test] Replace non-Standard "atomic_flag f(false);" with Standard "atomic_flag f;"
Summary:
Replace non-Standard "atomic_flag f(false);" with Standard "atomic_flag f;" in clear tests.
Although the value of 'f' is unspecified it shouldn't matter because these tests always call `f.test_and_set()` without checking the result, so the initial state shouldn't matter.
The test init03.pass.cpp is explicitly testing this non-Standard extension; It has been moved into the `test/libcxx` directory.
Reviewers: mclow.lists, STL_MSFT
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D19758
llvm-svn: 268355