Pull in pre-built library during edk2 build?

[Peter Hornyack <peterhornyack@google.com>]

I'd like to make an adjustment to the edk2 build (locally, not for
upstream) and I'm hoping someone can offer some guidance.

My goal is to pre-build an edk2 library in a separate build process,
then pull that library into the full build later on. Specifically I'm
building my firmware image using OvmfPkgX64.dsc, but I want to build
OpensslLib (CryptoPkg/Library/OpensslLib/OpensslLib.inf) in advance,
then pull the resulting lib into the full build later. How can I
achieve this?

In my build output I can see that when OpensslLib.inf is built, all of
the openssl .c files are compiled into .obj files, then an ar command
wraps those up into OpensslLib.lib. I want to pull those steps out and
pre-build OpensslLib.lib, but I've been unable to find where/how the
edk2 build grabs that .lib file and turns it into the final firmware
image. I've reviewed the edk2 build documentation but still can't
figure this out. Can anyone point me to the right place in the edk2
build files where I can make this happen? Or perhaps is there an
example of this already in the edk2 build that I can imitate?

Thanks,
Peter