msvc: ignore some libraries when linking

msvc: ignore some libraries when linking

To build with MSVC, we "translate" GCC options to MSVC options, and part
of those options refer to the libraries to link into the final
executable. Currently, this part looks somewhat like this on Windows:

	-lcurl -lnghttp2 -lidn2 -lssl -lcrypto -lssl -lcrypto -lgdi32
	-lcrypt32 -lwldap32 -lz -lws2_32 -lexpat

Some of those are direct dependencies (such as curl and ssl) and others
are indirect (nghttp2 and idn2, for example, are dependencies of curl,
but need to be linked in for reasons).

We already handle the direct dependencies, e.g. `-liconv` is already
handled as adding `libiconv.lib` to the list of libraries to link
against.

Let's just ignore the remaining `-l*` options so that MSVC does not have
to warn us that it ignored e.g. the `/lnghttp2` option. We do that by
extending the clause that already "eats" the `-R*` options to also eat
the `-l*` options.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>