fix libdispatch.a
fix libdispatch.a

The static version (`libdispatch.a`) that can be compiled using
`./configure --enable static=yes` was missing all the Swift overlay symbols
(everything in `swift_overlay.o`). The reason for that is that the linker is
invoked through libtool which wants `.lo` files but the Swift overlay got passed
as a `.o` file. This first of all leads to this warning:

    *** Warning: Linking the shared library libdispatch.la against the non-libtool
    *** objects [...]/swift_overlay.o is not portable!

And the result is that libtool doesn't include `swift_overlay.o` when putting
together the static library `libdispatch.a`.

This patch fixes this problem is a pretty crude way. The real problem is that
libtool doesn't understand Swift. So it can't be used when compiling
`swift_overlay.o`. In order to still get a `.lo` file this patch tricks libtool
into generating one from the `swift_overlay.o` generated by `swiftc`. It's very
hacky but I'm not sure what else to do.

Signed-off-by: Daniel A. Steffen <bc823475b60dbcbd7be1bbdfe095b5f1939d5bd2@apple.com>

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch