This patch makes sure that we always build the RPC server. The proposed
used for this is to begin integrating this server implementation into
`libomptarget`. That requires that we build this server ahead of time
when using a `LLVM_ENABLE_PROJECTS` build. Make a few tweaks to ensure
that the GCC compiler which may be used for this build doesn't complain.
Reviewed By: JonChesterfield
Differential Revision: https://reviews.llvm.org/D154105
df52a22b1b