gh-132026: Ensure _MIPS_SIM has defined _ABI identifiers for comparison (GH-132027)

When built on a MIPS architecture, `_MIPS_SIM` is used to determine
architecture specifics. The value is expected to match either
`_ABIO32`, `_ABIN32` or `_ABI64`.

In `gcc` config/mips/mips.h these values are defined as compiler
`builtin_define` inside of a switch/case. That means, mips64el and
mips64 architectures know about `_ABI64` but don't know about `_ABIO32`
and `_ABIN32`. In turn, when CPython tries to use them in comparison,
they may be undefined identifiers.

In default compiler behavior, the undefined identifier will be
evaluated as zero, and it will not match `_MIPS_SIM`. However, the
issues pop up when `-Wundef` (or, even worse, `-Werror=undef`) compiler
flag is enabled. Then suddenly it's visible as a warning or error.