[Scm-discuss] building SCM with recent GCC versions

[Steve VanDevender]

After upgrading my systems to the just-released Debian Buster with GCC
version 8.3, I found that rebuilding SCM with "gcc -O" produced a number
of test errors relating to floating-point printing and bignums.

After some trial and error and an inspired guess, I found that
"gcc -O -fwrapv" builds a version of SCM that compiles and passes all
tests.  This also produces working builds when higher optimization
levels like -O2 or -O3 are used.

"-fwrapv" tells GCC to assume that arithmetic "wraps around" mod 2^N
where N is the number of bits in an integer type.  This is apparently no
longer the default assumption in GCC.

I don't know yet which GCC versions might have this behavior other than
8.3.  "-fwrapv" has been an option for quite a while (I see it in a
system with GCC 4.4, at least).