Rename test.cc files to test.cpp.

The lit.cfg files only add .cpp to suffixes, so these tests used to never run,
oops.  (Also tweak to of these tests in minor ways to make the actually pass.)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224718 91177308-0d34-0410-b5e6-96231b3b80d8
Disable trigraphs in microsoft mode by default. Matches cl.exe.

The default value of Opts.Trigraphs now no longer depends solely on the
language input kind, so move the code out of setLangDefaults().  Also make
sure that Opts.MSVCCompat is set before the Trigraph code runs.

Related to PR21974.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224719 91177308-0d34-0410-b5e6-96231b3b80d8