GN: naive attempt for 32-bit Windows support

This uses the win_toolchain's SetEnv.cmd script to set up the environment for x86 builds.  Some of what it sets is redundant with what we set: include_dirs (INCLUDE), lib_dirs (LIB).  I'd sort of like to learn what parts of it actually matter: VSINSTALLDIR? VCINSTALLDIR? likely PATH?
This will not work for local builds not using win_toolchain.  I don't mind that too much, at least for now, maybe forever.  Most humans should be using 64-bit builds.

CQ_INCLUDE_TRYBOTS=master.client.skia.compile:Build-Win-MSVC-x86-Debug-Exceptions-Trybot,Build-Win-MSVC-x86_64-Debug-GN-Trybot,Build-Win-MSVC-x86_64-Release-GN-Trybot

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3257

Change-Id: Ib880fb738bc4b493e8905903706526110213be47
Reviewed-on: https://skia-review.googlesource.com/3257
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed