A bug in gdb is crashing when demangling some symbols. Gdb needs to be updated
to at least gdb 8.
Only run the debug build under gdb (other builds can time out).
* Remove cxx14 compatibility layer from ripple
* Update travis to clang 3.6 and drop gcc 4.8
* Remove unneeded beast CXX14 defines
* Do not run clang build with gdb with travis
* Update circle ci to clang 3.6 & gcc-5
* Don't run rippled in gdb, clang builds crash gdb
* Staticly link libstdc++, boost, ssl, & protobuf
* Support builds on ubuntu 15.10