This failure mode shows up occasionally when users try to include C headers in
C++ projects or when porting from Windows. We might as well recover in the way
the user expected, thus avoiding confusing diagnostic messages at point of use.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209963 91177308-0d34-0410-b5e6-96231b3b80d8

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209322 91177308-0d34-0410-b5e6-96231b3b80d8

Also flesh out missing tests, improve diagnostic QOI and fix a couple of corner
cases found in the process.

Fixes PR10606.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209276 91177308-0d34-0410-b5e6-96231b3b80d8

 - This is designed to make it obvious that %clang_cc1 is a "test variable"
   which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
   can be useful to redefine what gets run as 'clang -cc1' (for example, to set
   a default target).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@91446 91177308-0d34-0410-b5e6-96231b3b80d8

 - 'for i in $(find . -type f); do sed -e 's#\(RUN:.*[^ ]\) *&& *$#\1#g' $i | FileUpdate $i; done', for the curious.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@86430 91177308-0d34-0410-b5e6-96231b3b80d8

Tests and drivers updated, still need to shuffle dirs.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67602 91177308-0d34-0410-b5e6-96231b3b80d8

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@39734 91177308-0d34-0410-b5e6-96231b3b80d8