std.os.linux: Fix definition of tc_lflag_t on MIPS

[linusg]

[...]/std/os/linux.zig:6558:51: error: backing integer type 'c_uint' has bit size 32 but the struct fields have a total bit size of 33
pub const tc_lflag_t = if (is_mips) packed struct(tcflag_t) {
                                                  ^~~~~~~~

cc @alexrp

[alexrp]

Oops, thanks for catching this. Hopefully we can get MIPS in CI soon-ish.

[andrewrk]

Oops, thanks for catching this. Hopefully we can get MIPS in CI soon-ish.

Unfortunately LLVM has O(N^2) logic in their MIPS object file generation code, so I disabled MIPS testing in the CI. We can re-enable it by adding our own MIPS backend.