Move many configure checks to common.m4

Move many configure checks to common.m4

This moves many needed configure checks from gdb and gdbserver into
common.m4.  This helps gdbsupport, nat, and target be self-contained.

The result is a bit spaghetti-ish, because gdbsupport uses another m4
file from gdb/.  The resulting code is somewhat non-obvious.  However,
these problems already exist, so it's not really that much worse than
what is already done.

gdb/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.
	* configure.ac: Move many checks to ../gdbsupport/common.m4.

gdb/gdbserver/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.
	* configure.ac: Remove any checks that were added to common.m4.
	* acinclude.m4: Include lib-ld.m4, lib-prefix.m4, and
	lib-link.m4.

gdbsupport/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* configure, Makefile.in, aclocal.m4, common.m4, config.in:
	Rebuild.
	* common.m4 (GDB_AC_COMMON): Move many checks from
	gdb/configure.ac.
	* acinclude.m4: Include bfd.m4, ptrace.m4.

Change-Id: I931eaa94065df268b30a2f1354390710df89c7f8