RISCV single precision ABI is not supported

[zhaochenyuangit]

when compiling with the float abi lp64f, the current openlibm_fenv_riscv. header will raise the following error
single precision floating point ABI not supported
I did not see any point in forbidding using the single precision float point ABI, because riscv F and D extension share the same FCSR.
Is there any specific issue in using the single precision ABI?

P.S. the current riscv fenv support in openlibm is ported from freebsd/msun. However the github repo of freebsd does not have an issue tab, so I cannot get informative explanation there.

Best
Zhao