Touch up tests for new <version> header; fix module.modulemap.

This patch does some housekeeping for the new <version> header.
It adds it to the module.modulemap, and the double_include.sh.cpp test.

Additionally it corrects the // UNSUPPORTED options for the libc++
specific test. The header needs to compile under C++03 to support
modules, and it should compile under all available compilers.

llvm-svn: 329144