This was used for LoongArch64, where:
* `gnuf64` -> `ilp32d` / `lp64d` (full hard float)
* `gnuf32` -> `ilp32f` / `lp64f` (hard float for `f32` only)
* `gnusf` -> `ilp32` / `lp64` (soft float)
But Loongson eventually settled on just `gnu` for the first case since that's
what most people will actually be targeting outside embedded scenarios. The
`gnuf32` and `gnusf` specifiers remain in use.
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