This should fix #609
Not sure what the problem was, but we are not using functions from pg_bitutils, so just don't compile it.

For documentation purposes in case we need pg_bitutils later:
The problem potentially comes from either HAVE_X86_64_POPCNTQ or HAVE__BUILTIN_POPCOUNT.
We hard-code HAVE__BUILTIN_POPCOUNT to 1 in pg_config.h.in instead of checking if it is available, so that might be the issue. Cmake detects that HAVE_X86_64_POPCNTQ should be false, so I don't think it is related to HAVE_X86_64_POPCNTQ, but I can't be sure.

From the Yggdrasil build process with mingw:

[13:47:02] -- Looking for __get_cpuid
[13:47:03] -- Looking for __get_cpuid - found
[13:47:03] -- Performing Test HAVE_X86_64_POPCNTQ
[13:47:03] -- Performing Test HAVE_X86_64_POPCNTQ - Failed