Use -g flag instead of -gdwarf-2

Objects built with different debugging symbols formats don't play
together well.

Conflicts:
	engine/StirFile/Methcla.hs
Disable mpg123 for PNaCl library
Use clang to build on Android

Conflicts:
	engine/StirFile/Methcla.hs
Build boost::lockfree with std::atomics on Android

Conflicts:
	engine/external_libraries/boost/boost/lockfree/detail/atomic.hpp
Update stir

Conflicts:
	engine/external_libraries/stir
Use libmethcla from build directory on Android
Remove submodule catch
Update stir

Adapt to changes regarding build prefix argument to rule
functions.

Conflicts:
	engine/external_libraries/stir
Add ToBuildPrefix instance for Config
Use mkBuildPrefix for Android install path
Update stir

Also remove icecast targets

Conflicts:
	engine/external_libraries/stir
Update stir

Conflicts:
	engine/external_libraries/stir
Update stir

Conflicts:
	engine/StirFile/Methcla.hs
	engine/external_libraries/stir
Update stir

Conflicts:
	engine/external_libraries/stir
Get Freesound API key in Action instead of IO
Use command_ instead of deprecated system'

Conflicts:
	engine/StirFile/Methcla.hs
Return empty string if environment variable doesn't exist
Remove unused functions
Update stir

Conflicts:
	engine/external_libraries/stir
Depend on version of shake that includes getEnvWithDefault

Also bump dependency on stir.