build: build libdeflate with user selected C compiler
build: build libdeflate with user selected C compiler

If the user specified a C compiler, use it to build libdeflate.

Fixes #3978.
Message-Id: <31ce9ed80c81790116b6c2f9cab805d74dcbaddf@scylladb.com>

avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla