[clang] Get rid of "%T" expansions

[clang] Get rid of "%T" expansions

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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@310950 91177308-0d34-0410-b5e6-96231b3b80d8