Use IS_ABSOLUTE, rather than MATCHES "^/.*"
Remove usage of SSL_INCLUDE_DIRS macro, it is empty.
Remove workarounds for protobuf 2.6
Remove "/wd4267 /wd4244" flags, already done in cmake/os/Windows.cmake
Remove installation of gcc-4.8.1.tar.bz2

Change-Id: Ieb0872f4f5d986b577b0429bc748590e8f3bec13