[PATCH libassuan] Add fixes to support IBM z/OS platform.

[NIIBE Yutaka]

Sachin T wrote:
> Patch details -
> * m4/libtool.m4: use pass_all dependency checking on z/OS.
> * src/assuan-socket.c: Include sys/time.h header which defines fd_set, struct timeval.

Thank you for your report.

For the m4 change, I updated m4 (and build-aux) files from libgpg-error,
which should have same effect.

For the latter, I push the commit:

	c08091e84da7e39d0528ab9bd333818e58ab1beb

which include the header files when available.  I think that this
is better for other Operating Systems.
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