From Pere: go via TSystem to use prefix if defined (ROOT-6410).
Restore nested typedef fwd declaration construction.
Fix gcc48 ubuntu14 warning about maybe uninit vars

http://cdash.cern.ch/viewBuildError.php?type=1&buildid=67945
Cmake, gcc: use same opts for RELWITHDEBINFO and RELEASE

do not leverage Og as some differences with O2 might be there.
Changes to illustrate how to add a macro parameter in a test definition.
For roottest, implement NO_ROOTMAP option in REFLEX_GENERATE_DICTIONARY.
Fix for ROOT-6393
Add the -rdynamic flag, needed on cygwin to make symbols visible to dlsym
Use the official way of marking a variable used; else clang complains.
Improve SLoc and output for dynscope errors (more ROOT-6365).