Without the change `waf configure` hung on `i686Linux.samba` on systems
with large amount of host CPUs (for me it's 16).
This happens because one of the worker processes gets `-ENOMEM` and does
not recover from it:
2084476 mmap2(NULL, 8392704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = -1 ENOMEM (Cannot allocate memory)
2084476 munmap(0xf2b5c000, 16384) = 0
2084476 rt_sigprocmask(SIG_BLOCK, ~[RT_1], NULL, 8) = 0
2084476 madvise(0x1ff000, 8372224, MADV_DONTNEED) = 0
2084476 exit(0) = ?
2084476 +++ exited with 0 +++
THe change extends 32-bit arm workaround to limit to one thread to all
32-bit systems.
9e38b7b0fb