build: pass C compiler configuration in relocatable package build
build: pass C compiler configuration in relocatable package build

Just like we allow customizing the C++ compiler, we should allow customizing
the C compiler.

Ref #3978
Message-Id: <f628708a6781c3cd8ea71bc0bb483cc500bc0c93@scylladb.com>

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