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 * }

test/libcxx/double_include.sh.cpp

@@ -129,6 +129,7 @@
 #include <valarray>
 #include <variant>
 #include <vector>
+#include <version>
 #include <wchar.h>
 #include <wctype.h>
 

test/libcxx/language.support/support.limits/version.pass.cpp

@@ -8,9 +8,6 @@
 //===----------------------------------------------------------------------===//
 
 // <version>
-// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
-// UNSUPPORTED: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7
-// UNSUPPORTED: clang-3.8, clang-3.9, clang-4.0, clang-5.0, clang-6.0
 
 #include <version>