The %T lit expansion expands to a common directory shared between all the tests in the same directory, which is unexpected and unintuitive, and more importantly, it's been a source of subtle race conditions and flaky tests. In https://reviews.llvm.org/D35396, it was agreed that it would be best to simply ban %T and only keep %t, which is unique to each test. When a test needs a temporary directory, it can just create one using mkdir %t.
This patch removes %T in clang.
Differential Revision: https://reviews.llvm.org/D36437
llvm-svn: 310950
Differential Revision: http://reviews.llvm.org/D19843
Corresponding LLVM change: http://reviews.llvm.org/D19842
Re-commit after addressing issues with of generating too many warnings for Windows and asan test failures.
Patch by Eric Niebler
llvm-svn: 272562