Introduce the feature "can-remove-opened-file" to suppress tests. [PR18856]

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201482 91177308-0d34-0410-b5e6-96231b3b80d8
check-clang: Introduce the feature "dw2" to suppress CodeGenCXX/debug-info-namespace.cpp with *-win32.

FIXME: Could we add itanium triple here?

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201483 91177308-0d34-0410-b5e6-96231b3b80d8
check-clang: Introduce the feature "non-ms-sdk" to suppress Driver/nostdincxx.cpp on msvc.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201484 91177308-0d34-0410-b5e6-96231b3b80d8
clang/unittests/AST,ASTMatchers: Remove _MSC_VER.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201485 91177308-0d34-0410-b5e6-96231b3b80d8