Check for sigprocmask in common.m4

I noticed that gdbsupport uses HAVE_SIGPROCMASK, but common.m4 does
not check for it.  This means that gdbserver may not compile some
gdbsupport code properly.  This patch fixes this error.

gdb/ChangeLog
2019-10-23  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.
	* configure.ac: Don't check for sigprocmask.
	* gdbsupport/common.m4 (GDB_AC_COMMON): Check for sigprocmask.

gdb/gdbserver/ChangeLog
2019-10-23  Tom Tromey  <tom@tromey.com>

	* configure, config.in: Rebuild.

Change-Id: I2c0a4dd2c376507b9483b38707a242382faa8163