Let's audit the CMakeLists.txt of kms_message. I'm hazy on how the install targets and package configuration work.

kms_message won't (for now) be distributed as a separate library. It will be statically linked with libmongocrypt. Really, we just need it to work well enough so we can statically link against it everywhere we build libmongocrypt. This ticket might be a no-op, but let's at least spend some time double checking this.