sh4 support

sh4 support

Forwarded: not yet.
BTS: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1027168

onetbb currently FTBFS on sh4 because the source code assumes that the target
FPU supports all four rounding modes (FE_TONEAREST, FE_DOWNWARD, FE_UPWARD and
FE_TOWARDZERO) which is not the case on sh4 which supports FE_TONEAREST and
FE_TOWARDZERO only [1].

The attached patch fixes these assumptions for sh4 and makes the code build. I
have already patched and uploaded the package to the unreleased distribution
so that the mold linker can build on sh4 as well.

I will forward the patch later after reformating it.
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Gbp-Pq: Name sh4-support.patch