Sysdeps ordering

[Jeff Bailey]

I just noticed this when configuring for i386-gnu:

running configure fragment for ../libc/sysdeps/mach/hurd
checking Hurd header version... ok
checking whether  supports the retcode keyword... no
running configure fragment for ../libc/sysdeps/mach 
checking for mig... mig

Now that the the mig check has moved to the mach configure fragment, the
hurd configure fragment no longer has the information to test if the
retcode keyword is supported.

I'm not sure the best way to reorder these, and having the mig test in
sysdeps/mach/hurd doesn't seem right either.

Tks,
Jeff Bailey