Fix erroroneous use of '%zu' in elfcore_grok_win32pstatus

Fix erroroneous use of '%zu' in elfcore_grok_win32pstatus

As reported in [1], _bfd_error_handler() doesn't support '%zu'.

module_name_size is always 32-bits in the data structure we are
extracting it from, so use an unsigned int to store it instead.

[1] https://sourceware.org/pipermail/gdb-patches/2020-August/171391.html

bfd/ChangeLog:

2020-08-21  Jon Turney  <jon.turney@dronecode.org.uk>

	* elf.c (elfcore_grok_win32pstatus): Change name_size to unsigned
	int. Use '%u' format with  _bfd_error_handler to render it.