Create .gyp rules for shaderc libraries

To build shaderc, gyp used to punt to cmake, which did not work well on the bots and I couldn't find any way to pipe the variables into cmake which would have made it happy.

So, I wrote a gyp file for shaderc and its dependencies.  Nothing super complicated (thank goodness), except for the files that spirv-tools needed generated.

BUG=skia:5186
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2047833003

Review-Url: https://codereview.chromium.org/2047833003
1 file changed