Make cc_library(alwayslink=True) apply to .a in srcs

[keith]

Previously if you had an archive in the srcs of a cc_library and set
alwayslink=True that was ignored. You had to have named the library .lo
(arguably an implementation detail) to get the desired behavior.

[keith]

I'm curious to hear from folks with more context on if this is a good idea to change. previously if you had both .a and .c files in srcs, alwayslink would only apply to the .c files, which might have been intentional-ish. But on the other hand I think this behavior was surprising in the opposite way. (previously the workaround would be to use cc_import(alwayslink=True))

[keith]

i will exclude from CI if we get consensus on this being a good idea