Even though Makefile.inc sets COMPILERC=ports-gcc, this is not enough to
disable asterisk on archs without ports-gcc support, because
Makefile.inc includes bsd.port.arch.mk before compiler.port.mk restricts
the available archs with ONLY_FOR_ARCHS.
This is a workaround to get rid of useless build failures on riscv64.
ok sthen@ (maintainer)