Drivers that don't support GL_ARB_shading_language_420pack require that
the storage qualifier be specified even when inside an interface block.

AMD's driver throws a compile error when "centroid in/out" is used within
an interface block.

Our previous behavior was to include the storage qualifier regardless, but
this wasn't working on AMD, therefore we should check for the presence of
the extension and include based on this, instead.

OS X's shader compiler has a bug with interface blocks where interface block members don't properly inherit the layout qualifier from the interface
block.
Work around this limitation by explicitly stating the layout qualifier on both the interface block and every single member inside of that block.

Also remedies places where the video backends and core rely on things
being indirectly included.

This fixes the crashes occuring at startup with a non-empty shader cache.
Because LinearDiskCache reads/writes to the storage of ShaderUid, ShaderUid must be trivially copyable.
Additionally, adds a static assert to LinearDiskCache to ensure this doesn't happen in the future.

The initialization of ShaderUid data has been moved to the code generation functions, so the above condition holds true.

Functions defined in a header should be inline only, otherwise program
code is generated for every other file that calls said functions

Note that the "this" implicit argument counts as 1, which is why all the
printf arguments are shifted over one.