Apply fragment color broadcasting to secondary outputs When GL_EXT_draw_buffers is enabled, gl_FragColor is replaced with gl_FragData. Apply the same transformation to gl_SecondaryFragColorEXT if it is statically used to avoid compiler failures. Bug: angleproject:1085 Change-Id: If154cd20a8e14a92da520847a9c4508971a45fef Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4900641 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>