Whilst the commit message documented some of the details, I had intended
to include this comment in the actual header, but failed to amend the
commit properly.
Fixes: 9e5b0d9eac ("cross-build: Fix bmake bootstrap with glibc 2.34")
MFC after: 1 week
As of glibc 2.34, our unistd.h wrapper's inclusion of stdlib.h exposes
fragility in glibc's sys/wait.h and corresponding part of stdlib.h,
leading to "error: use of undeclared identifier 'WNOHANG'" and similar
errors when bootstrapping bmake.
Work around this by wrapping sys/wait.h to force stdlib.h's inclusion
first before it's implicitly included during the problematic window in
sys/wait.h.
MFC after: 1 week
