gdbsupport/common.m4: check for sigtimedwait

The next patch will make the use of sigtimedwait conditional to whether
the platform provides it.  Start by adding a configure check for it.

gdbsupport/ChangeLog:

	* common.m4 (GDB_AC_COMMON): Check for sigtimedwait.
	* config.in, configure: Re-generate.

gdb/ChangeLog:

	* config.in, configure: Re-generate.

gdbserver/ChangeLog:

	* config.in, configure: Re-generate.

Change-Id: Ic7613fe14521b966b4d991bbcd0933ab14629c05