fix passing long argument lists to the linker, PR 15171, take 2

[Nathan Froyd]

Hi!

This patch addresses PR 15171 by checking if we're constructing a
too-long argument list for the linker and writing it to a response file
if the linker supports it.  A test case is included that should test the
newly-added behavior on at least some Windows checkouts (depending on
where the checkout lives on disk).  It doesn't appear that there's any
tests that clang parses a response file, so this test takes care of that
too.

Tested on linux x86-64.

-Nathan
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