New release portability issue

[Dennis Clarke]

     On an old Fujitsu SPARC64 server running Solaris 10 there is no 
builtin compiler function for __builtin_popcount. This seems to be
something new in libcrux_mlkem768_sha3.h header. There was no issue
with openssh-9.8p1.

     The LLVM folks have neat little bit of code that can do the bit
shifting and adding :

 
https://github.com/llvm-mirror/compiler-rt/blob/master/lib/builtins/popcountdi2.c

     It would be better to use inline asm where the SPARC64 hardware does
indeed have the popc instruction.



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Dennis Clarke
RISC-V/SPARC/PPC/ARM/CISC
UNIX and Linux spoken