Get rid of -Wodr warning (PR build/23399)

Get rid of -Wodr warning (PR build/23399)

The PR reports that building with -Wodr -flto complains about different
versions of struct ipa_sym_addresses, in common/agent.c and
gdbserver/tracepoint.c.  This patch renames the version in common to
ipa_sym_addresses_common to avoid the name clash.  Because the IPA_SYM
assumed the name ipa_sym_addresses, it now requires the includer to
define the IPA_SYM_STRUCT_NAME macro to define the name of the structure
holding the IPA symbol addresses.

gdb/ChangeLog:

	PR build/23399
	* common/agent.c (IPA_SYM_STRUCT_NAME): Define.
	(struct ipa_sym_addresses): Rename to...
	(struct ipa_sym_addresses_common): ... this.
	* common/agent.h (IPA_SYM): Use IPA_SYM_STRUCT_NAME.

gdb/gdbserver/ChangeLog:

	PR build/23399
	* tracepoint.c (IPA_SYM_STRUCT_NAME): Define.