libctf: lookups by name and symbol

libctf: lookups by name and symbol

These functions allow you to look up types given a name in a simple
subset of C declarator syntax (no function pointers), to look up the
types of variables given a name, and to look up the types of data
objects and the type signatures of functions given symbol table offsets.

(Despite its name, one function in this commit, ctf_lookup_symbol_name(),
is for the internal use of libctf only, and does not appear in any
public header files.)

libctf/
	* ctf-lookup.c (isqualifier): New.
	(ctf_lookup_by_name): Likewise.
	(struct ctf_lookup_var_key): Likewise.
	(ctf_lookup_var): Likewise.
	(ctf_lookup_variable): Likewise.
	(ctf_lookup_symbol_name): Likewise.
	(ctf_lookup_by_symbol): Likewise.
	(ctf_func_info): Likewise.
	(ctf_func_args): Likewise.

include/
	* ctf-api.h (ctf_func_info): New.
	(ctf_func_args): Likewise.
	(ctf_lookup_by_symbol): Likewise.
	(ctf_lookup_by_symbol): Likewise.
	(ctf_lookup_variable): Likewise.