This test was previously passing because myabs was actually emitted into the
debug information and we called that. The test itself was broken as it didn't
use the libc++ directory structure (the /v1/ directory was just called /include/).
This patch gives myabs a default argument which we can't get from debug information
and inlines the function to make sure we can't call it from LLDB without loading
the C++ module.
llvm-svn: 374335