fill-outline-color render tests failing locally on OS X

[jfirebaugh]

The following render tests, which were unignored as part of #6899, are failing locally for me on OS X, although they are passing on OS X CI:

• failed fill-outline-color function
• failed fill-outline-color literal
• failed fill-outline-color multiply
• failed fill-outline-color opacity
• failed regressions mapbox-gl-js#2305

Here's what the first one looks like:

Expected

Actual

Diff

The diff on macOS CI, where these are passing, is:

I'm currently at 6c30105 and mapbox/mapbox-gl-test-suite@d27aab1, macOS 10.11.6 (15G1108).

[jfirebaugh]

At least part of the difference seems to be due to the following:

• Mapbox GL JS renders both fill outline (when fill-outline-color is set) and fill antialias (when it isn't) after the fill.
• Mapbox GL Native renders fill outline before the fill, or fill antialias after.

When I change native to work like js does, it reduces the difference to:

But the corners are still off.

[jfirebaugh]

The remaining difference is due to glLineWidths other than 1 not being supported by the headless rendering in GL-JS test environment.

[kkaefer]

Fixed in #9699