gimp: work around problems with cc -v + cwrappers appending link flags

As ryoon@ reported to me after I committed a bit more MKRELRO churn,
ensuring RELRO is always applied through the compiler wrappers causes
a build failure.

This is because GIMP is attempting to parse the output of gcc --version,
which returns an error message (indicating a link failure of a nonexistent
program) alongside the version information when -Wl,-zrelro is appended
or prepended through cwrappers.

So, we use -c to avoid linking the nonexisting program we are "compiling".

(nia)