Move event-loop.[ch] to gdbsupport/

Move event-loop.[ch] to gdbsupport/

This moves event-loop.[ch] to gdbsupport/ and updates the uses in gdb.

gdb/ChangeLog
2020-04-13  Tom Tromey  <tom@tromey.com>

	* run-on-main-thread.c: Update include.
	* unittests/main-thread-selftests.c: Update include.
	* tui/tui-win.c: Update include.
	* tui/tui-io.c: Update include.
	* tui/tui-interp.c: Update include.
	* tui/tui-hooks.c: Update include.
	* top.h: Update include.
	* top.c: Update include.
	* ser-base.c: Update include.
	* remote.c: Update include.
	* remote-notif.c: Update include.
	* remote-fileio.c: Update include.
	* record-full.c: Update include.
	* record-btrace.c: Update include.
	* python/python.c: Update include.
	* posix-hdep.c: Update include.
	* mingw-hdep.c: Update include.
	* mi/mi-main.c: Update include.
	* mi/mi-interp.c: Update include.
	* main.c: Update include.
	* linux-nat.c: Update include.
	* interps.c: Update include.
	* infrun.c: Update include.
	* inf-loop.c: Update include.
	* event-top.c: Update include.
	* event-loop.c: Move to ../gdbsupport/.
	* event-loop.h: Move to ../gdbsupport/.
	* async-event.h: Update include.
	* Makefile.in (COMMON_SFILES, HFILES_NO_SRCDIR): Update.

gdbsupport/ChangeLog
2020-04-13  Tom Tromey  <tom@tromey.com>

	* event-loop.h: Move from ../gdb/.
	* event-loop.cc: Move from ../gdb/.