Synthetic values are now automatically enabled and active by default. SBValue...

Synthetic values are now automatically enabled and active by default. SBValue is set up to always wrap a synthetic value when one is available.
A new setting enable-synthetic-value is provided on the target to disable this behavior.
There also is a new GetNonSyntheticValue() API call on SBValue to go back from synthetic to non-synthetic. There is no call to go from non-synthetic to synthetic.
The test suite has been changed accordingly.
Fallout from changes to type searching: an hack has to be played to make it possible to use maps that contain std::string due to the special name replacement operated by clang
Fixing a test case that was using libstdcpp instead of libc++ - caught as a consequence of said changes to type searching

llvm-svn: 153495