Ports using USES=compiler:c11, for instance, devel/libffi (needed for Python), imply lang/gcc9, which is set to IGNORE on MIPS, "is only for aarch64 amd64 arm armv6 armv7 i386 powerpc powerpc64 sparc64, while you are running mips64". This prevents, among others, python (default 3.x version) and mail/fetchmailconf to be built.
Moin moin Closing this due to old age. Please re-open if it is still an relevant. mfg Tobias