gdbserver/IPA: Export some functions via global function pointers.

gdbserver/IPA: Export some functions via global function pointers.

On powerpc64, qSymbol for a function returns the function code address,
and not the descriptor address.  Since we emit code calling gdb_collect
and some other functions, we need the descriptor (no way to know the
proper TOC address without it).  To get the descriptor address, make
global function pointer variables in the IPA pointing to the relevant
functions and read them instead of asking for them directly via qSymbol.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-ipa.c: Rename gdb_agent_get_raw_reg to get_raw_reg.
	* linux-amd64-ipa.c: Likewise.
	* linux-i386-ipa.c: Likewise.
	* linux-s390-ipa.c: Likewise.
	* tracepoint.c: IPA-export gdb_collect_ptr instead of gdb_collect,
	ditto for get_raw_reg_ptr, get_trace_state_variable_value_ptr,
	set_trace_state_variable_value_ptr.
	(struct ipa_sym_addresses): Likewise.
	(symbol_list): Likewise.
	(install_fast_tracepoint): Dereference gdb_collect_ptr instead of
	accessing gdb_collect directly.
	(gdb_collect_ptr_type): New typedef.
	(get_raw_reg_ptr_type): New typedef.
	(get_trace_state_variable_value_ptr_type): New typedef.
	(set_trace_state_variable_value_ptr_type): New typedef.
	(gdb_collect_ptr): New global.
	(get_raw_reg_ptr): New global.
	(get_trace_state_variable_value_ptr): New global.
	(set_trace_state_variable_value_ptr): New global.
	(get_raw_reg_func_addr): Dereference get_raw_reg_ptr instead of
	accessing get_raw_reg directly.
	(get_get_tsv_func_addr): Likewise for
	get_trace_state_variable_value_ptr.
	(get_set_tsv_func_addr): Likewise for
	set_trace_state_variable_value_ptr.
	* tracepoint.h: Rename gdb_agent_get_raw_reg to get_raw_reg.