Consolidate headers:
- Group src/common/*.h in src/common/Common.h
- Include all C and C++ standard library headers in q_shared.h
Merge branch 'master' into engine-upgrade/headers
Merge branch 'master' into engine-upgrade/headers

Conflicts:
	src/common/Command.h
	src/common/LineEditData.cpp
	src/common/LineEditData.h
	src/common/String.h
	src/engine/framework/CommandSystem.cpp
	src/engine/framework/CvarSystem.cpp
	src/engine/qcommon/files.cpp
	src/engine/sys/sdl_snd.cpp
Merge branch 'master' into engine-upgrade/headers

Conflicts:
	src/engine/audio/AudioPrivate.h
	src/engine/framework/FileSystem.cpp
	src/engine/rendererGL/tr_animation.cpp
	src/engine/rendererGL/tr_backend.cpp
	src/engine/rendererGL/tr_bsp.cpp
	src/engine/rendererGL/tr_image.cpp
	src/engine/rendererGL/tr_light.cpp
	src/engine/rendererGL/tr_model.cpp
	src/engine/rendererGL/tr_shade.cpp
	src/engine/rendererGL/tr_shade_calc.cpp
	src/engine/sys/sdl_glimp.cpp
Merge branch 'nacl' into engine-upgrade/headers

Conflicts:
	src/common/Command.cpp
	src/common/RPC.h
	src/engine/qcommon/qcommon.h
	src/engine/sys/con_curses.cpp
Fix client build
Merge branch 'master' into headers

Conflicts:
	src/common/CommonSyscalls.h
	src/common/FileSystem.cpp
	src/common/FileSystem.h
	src/common/IPC.h
	src/engine/audio/ALObjects.h
	src/engine/audio/AudioPrivate.h
	src/engine/audio/snd_codec_ogg.cpp
	src/engine/framework/VirtualMachine.cpp
	src/engine/framework/VirtualMachine.h
	src/engine/server/sv_ccmds.cpp
	src/engine/server/sv_game.cpp
First working PoC of precompiled headers.

There are many problems:
- Only works on Clang
- Instead of the obj, makes the source file depend on the PCH
- No way to deactivate PCH
- Only for client / ttyclient / server

But at least it compiles faster.
Clean up a few more includes
Add PCH for everything except QVM and nexe

* Compile libraries for which we have the source in their own static lib
* Make the -include foo.pch option a target option instead of a source file one
* Detect if a target needs to be compiled with -fPIC (shared libs)
Add GCC support and fix link errors
Add support for multiple configurations, and some misc fixes
Merge branch 'master' into headers
Fix compilation on MinGW
Add support for slim LTO objects, also fixes GCC 4.9 LTO which uses slim objects by default
Fix log level names to avoid conflicts with macros
Add MSVC support for PCH
Merge branch 'headers'