Improve error reporting in the Windows port when env size is too large.
w32/subproc/misc.c (arr2envblk): Compute and return the size of
the environment passed to child process.
w32/subproc/sub_proc.c (process_begin): If the call to
CreateProcess failed with EINVAL, and the required environment
size was larger than 32KB, assume it's a Windows XP limitation,
and display an error message to that effect.
w32/subproc/proc.h (arr2envblk): Update prototype.
Copyright-paperwork-exempt: yes
3 files changed
