Move errno.h to common-defs.h

This commit moves the inclusion of errno.h to common-defs.h and
removes all other inclusions.  Note that prior to this commit errno.h
was included unconditionally in defs.h, whereas in common-defs.h it is
protected by "#ifdef HAVE_ERRNO_H".  This does not change the status
quo, since presumably every platform on which GDB builds has errno.h.

gdb/
2014-07-30  Gary Benson  <gbenson@redhat.com>

	* configure.ac (AC_CHECK_HEADERS): Add errno.h.
	* configure: Regenerate.
	* config.in: Likewise.
	* common/common-defs.h: Include errno.h.
	* defs.h: Do not include errno.h.
	* ada-typeprint.c: Likewise.
	* c-typeprint.c: Likewise.
	* core-regset.c: Likewise.
	* corefile.c: Likewise.
	* corelow.c: Likewise.
	* event-loop.c: Likewise.
	* f-typeprint.c: Likewise.
	* gnu-nat.c: Likewise.
	* go32-nat.c: Likewise.
	* i386gnu-nat.c: Likewise.
	* m2-typeprint.c: Likewise.
	* nat/linux-btrace.c: Likewise.
	* p-typeprint.c: Likewise.
	* procfs.c: Likewise.
	* remote-sim.c: Likewise.
	* rs6000-nat.c: Likewise.
	* target.c: Likewise.
	* typeprint.c: Likewise.
	* ui-file.c: Likewise.
	* valops.c: Likewise.
	* valprint.c: Likewise.

gdb/gdbserver/
2014-07-30  Gary Benson  <gbenson@redhat.com>

	* server.h: Do not include errno.h.
	* event-loop.c: Likewise.
	* hostio-errno.c: Likewise.
	* linux-low.c: Likewise.
	* remote-utils.c: Likewise.
	* spu-low.c: Likewise.
	* utils.c: Likewise.