We cannot filter all libraries because duplicate -l flags have a semantic meaning based on their order, but filtering out just the common Swift libraries should yield a good size improvement already and is safe.
Otherwise we can duplicate linker flags across input binaries, which can result in very large linkerr invocation commands.
Resolves https://github.com/apple/swift/issues/58380
Two tests used -emit-library with the same module name and without an
explicit -o path, meaning that the output would go into whatever
lit.py was using as its working directory. If the tests ran at exactly
the same time, they could contend for the output file. We don't actually
use the built library at all in the test, so just drop the -emit-library
entirely.
Also, remove an unused compilation step from another test, which just
checks what happens when swift-autolink-extract doesn't use any
arguments.
rdar://problem/39510413
Cygwin and MinGW should use the autolink feature in the sameway of Linux
due to the linker's limit. Now swift-autolink-extract recognizes the
COFF format file for Cygwin/MinGW.
