Bitsize-specific libraries in NaCl GYP projects

[Ian Lewis (Google)]

I've been working with Brad Nelson to try and improve the situation
for 64-bit Windows-based GYP builds. He's made some improvements and
we can now build both 32 and 64 bit targets.

However, there is one thing that GYP can't do--not because we don't
want it to, but because XCode and Visual Studio are both less-than-
great at this: providing libraries that build *only* in one
configuration.

In other words, it's possible to have (for example)
service_runtime_x86 build as a 32 bit target and a 64 bit target. But
it's difficult to have a library called service_runtime_x86_32 that
only builds for 32 bit targets, and another one called
service_runtime_x86_64 that only builds for 64 bits.

The suggestion from the Chromium team is to build all libraries for
all targets, and use #ifdefs to switch sections of code in and out.
This isn't quite as elegant as the existing solution, but it's
straightforward. Fortunately the amount of code affected is extremely
small and largely limited to a handful of .S files.

Over the next day or two I expect to modify the GYP build to eliminate
the subarchitecture-specific libraries. Please let me know if you have
questions or concerns.
Thanks
Ian