Improve recompile speed: Don't include git_revision.h in system.h (leads to excessive recompiles)
[Win32] Remove condition `!defined(_LIB)` for git_revision.h inclusion

XBMC seems to compile and display a git revision with or without this condition.

This reverts the change to PlatformInclude.h (now GitRevision.cpp) in b4952cf
[ios/atv2/osx] - sync xcode project
Merge pull request #2866 from garbear/git_rev

Improve recompile speed: Don't include git_rev.h/git_revision.h in system.h