Remove newlines from warnings

ARI pointed out that a recent patch introduced a call to "warning"
with a string that ended in a newline:

    https://sourceware.org/ml/gdb-patches/2019-06/msg00000.html

This is generally forbidden, I believe, because warning adds its own
newline.

This patch removes all of the trailing newlines I was able to find.  I
searched for 'warning (.*\\n"' and then fixed the ones where the
newline appeared at the end of the string (some had internal
newlines).

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-06-10  Tom Tromey  <tromey@adacore.com>

	* m32c-tdep.c (m32c_m16c_address_to_pointer): Don't end warning
	with a newline.
	* guile/guile.c (handle_boot_error): Don't end warning with a
	newline.
	* cli/cli-cmds.c (exit_status_set_internal_vars): Don't end
	warning with a newline.
	* s12z-tdep.c (s12z_skip_prologue): Don't end warning with a
	newline.
	(s12z_frame_cache): Likewise.
	* dwarf-index-cache.c (index_cache::store): Don't end warning with
	a newline.
	* solib-svr4.c (disable_probes_interface): Don't end warning with
	a newline.
	* nat/fork-inferior.c (fork_inferior): Don't end warning with a
	newline.
	* python/python.c (do_finish_initialization): Don't end warning
	with a newline.

gdb/gdbserver/ChangeLog
2019-06-10  Tom Tromey  <tromey@adacore.com>

	* remote-utils.c (look_up_one_symbol, relocate_instruction): Don't
	end warning with a newline.
	* linux-s390-low.c (s390_get_wordsize): Don't end warning with a
	newline.
	* thread-db.c (attach_thread): Don't end warning with a newline.
	(thread_db_notice_clone): Likewise.
	* tracepoint.c (gdb_agent_helper_thread): Don't end warning with a
	newline.
	* linux-x86-low.c (x86_get_min_fast_tracepoint_insn_len): Don't
	end warning with a newline.