[TestRvalueReferences] Fix an expectation.

Summary:
If 'i' is an rvalue reference to an 'int', evaluating it with the
'expression' command will return an 'int' value and not an 'int &&'.
Before this patch, an 'int &&' type was expected.

Enabled the test for clang and gcc as all parts of the test now pass
when the testcase is compiled with them.

Test Plan: dotest.py -C <gcc|clang> -p TestRvalueReferences

Reviewers: spyffe, chaoren

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9005

llvm-svn: 235036