I've just tried to build Python with {C,CXX,LD}FLAGS set to '-flto'.

Unfortunately following conftest source file is fragile:

cat /tmp/mc.c
int
main ()
{

  unsigned int fpcr;
  __asm__ __volatile__ ("fmove.l %%fpcr,%0" : "=g" (fpcr));
  __asm__ __volatile__ ("fmove.l %0,%%fpcr" : : "g" (fpcr));

  ;
  return 0;
}

gcc --version:
gcc (GCC) 5.1.1 20150424 (prerelease)

gcc -c /tmp/mc.c
/tmp/mc.c: Assembler messages:
/tmp/mc.c:6: Error: no such instruction: `fmove.l %fpcr,%eax'
/tmp/mc.c:7: Error: no such instruction: `fmove.l -4(%rbp),%fpcr'

gcc -flto -c /tmp/mc.c

As GCC does not produce assembly with -flto and -c (unless you append -ffat-lto-objects), the compilation success.

Can you please write more robust configuration.
Thanks,
Martin