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.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329144 91177308-0d34-0410-b5e6-96231b3b80d8

include/module.modulemap

@@ -470,6 +470,10 @@ module std [system] {
     export initializer_list
     export *
   }
+  module version {
+    header "version"
+    export *
+  }
 
   // FIXME: These should be private.
   module __bit_reference { header "__bit_reference" export * }