libiberty: On Windows, pass a >32k cmdline through a response file.

pex-win32.c (win32_spawn): If the command line for CreateProcess
exceeds the 32k Windows limit, try to store it in a temporary
response file and call CreateProcess with @file instead (PR71850).

Signed-off-by: Costas Argyris <costas.argyris@gmail.com>
Signed-off-by: Jonathan Yong <10walls@gmail.com>

libiberty/ChangeLog:

	* pex-win32.c (win32_spawn): Check command line length
	and generate a response file if necessary.
	(spawn_script): Adjust parameters.
	(pex_win32_exec_child): Ditto.

Signed-off-by: Jonathan Yong <10walls@gmail.com>