GN: components as static library instead of source set

This also puts the .a in the top-level of the ouptut directory, just
like we do for .so files.  It's less required than for .sos, but it
does make it easier to find the .a.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2197633002

Review-Url: https://codereview.chromium.org/2197633002
2 files changed