for preprocessing

r300667 added support for editor placeholder to Clang. That commit didn’t take
into account that users who use Clang for preprocessing only (-E) will get the
"editor placeholder in source file" error when preprocessing their source
(PR33394). This commit ensures that Clang doesn't lex editor placeholders when
running a preprocessor only action.

rdar://32718000

Differential Revision: https://reviews.llvm.org/D34256


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305576 91177308-0d34-0410-b5e6-96231b3b80d8