Reenable yasm for Android x86 and x86-64 on Linux host

Reenable yasm for Android x86 and x86-64 on Linux host

It turns out that gyp (kind of) has support for cross
compiling with a different host and target.  We simply
need to specify CC_host and CC_target instead of CC.

Making this change allows us to compile yasm on a Linux
host for Android.

We run into problems on Mac because
the linker on a Mac host requires different command line
arguments than the linker on the Android target.  In
looking through the code for gyp itself and speaking to
Ben, it doesn't appear to me that gyp supports passing
different arguments to host and target linkers.

I would imagine that we would have similar problems on
Windows.

Below is a link to a CL that would fix this issue in gyp.
It looks like it has been dropped for a long time.
Thanks to Ben for this link!
https://chromiumcodereview.appspot.com/10795044/

Also I'm adding a link to the build instructions for Chrome
(thanks again Ben).  It looks like they only support
building for Android from Linux.
https://code.google.com/p/chromium/wiki/AndroidBuildInstructions

My next steps are:
1) Getting in touch with Torne or someone else with gyp to
see if people are aware of this issue or interested in
fixing it.
2) Deciding if skia should care about this issue.
3) Deciding if skia should work around this issue.

It'd be really great to hear your thoughts on (2) and (3).
My first thought is that we shouldn't care because, as
long as we always compile the production copy of skia for
Android on Linux, we will get the fast code.  Is this
a valid conclusion?  Is there a way to write Android apps
on Mac that accidentally use the slower code?

If we do care, there are workarounds:
For Mac, we can check in a yasm binary - it's a little
smaller than the one I am deleting in this CL :-/
For Windows, we *might* be able to use the yasm.exe binary
already in externals (we get this from DEPS because this is
how chromium uses yasm on Windows).
Are there other platforms that we care about?

Let me know what you think!

BUG=skia:4028
DOCS_PREVIEW= https://skia.org/?cl=1239333002

Review URL: https://codereview.chromium.org/1239333002