build: Lower-case names of four .lib files

We refer to these by their all-lower-case names in other .gn files,
and the on-disk case in at least the hermetic toolchain we use is
all-lower-case.

This should let us use lld-link `/reproduce:` tar files without a
ciopfs mount when cross-linking from linux with a case-sensitive
file system.

No behavior change for regular builds.

Bug: none
Change-Id: I24eff07a8e52ab7c07fb70950294910bca57c3f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6824473
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1498381}