Changes needed because of changes in the API for clang v3.5
Merge pull request #5403 from gartung/clangSA-clang-3.5-api-change

Changes needed because of changes in the API for clang v3.5
Get clang to compile DataFormat/Math.
More clang fixes.
Even more clang fixes.
Limit damage from various vpp_generated.cpp

For some reason, even with -O1, vpp_generated.cpp take huge amount of
memory to compile.
Fix clang errors / warnings.

- These have been introduced recently. C++14 cannot come early enough.
Allow clang workaround to coexists with gcc flags.
Get ExtVec to compile properly with gcc.