Include common-defs.h instead of defs.h/server.h in shared code

Include common-defs.h instead of defs.h/server.h in shared code

This commit makes 19 of the 22 shared .c files in common, nat and
target include common-defs.h instead of defs.h/server.h.  The
remaining three files need slight extra work and are dealt with
in separate commits.

gdb/ChangeLog:

	* common/agent.c: Include common-defs.h.
	Don't include defs.h or server.h.
	* common/buffer.c: Likewise.
	* common/common-debug.c: Likewise.
	* common/common-utils.c: Likewise.
	* common/errors.c: Likewise.
	* common/filestuff.c: Likewise.
	* common/format.c: Likewise.
	* common/gdb_vecs.c: Likewise.
	* common/print-utils.c: Likewise.
	* common/ptid.c: Likewise.
	* common/rsp-low.c: Likewise.
	* common/signals.c: Likewise.
	* common/vec.c: Likewise.
	* common/xml-utils.c: Likewise.
	* nat/linux-osdata.c: Likewise.
	* nat/linux-procfs.c: Likewise.
	* nat/linux-ptrace.c: Likewise.
	* nat/mips-linux-watch.c: Likewise.
	* target/waitstatus.c: Likewise.