libsysprof: add versioning macros

This also moves stackstash.[ch] into a location that can be
embedded by both the libsysprof and libsysprof-ui code. We
pass native pointers to the structure as a gpointer in the
public API to allow for this. The performance of that code is
incredibly sensitive to the interactivity of Sysprof.

src/libsysprof/elfparser.h

@@ -54,4 +54,3 @@ gulong        elf_parser_get_sym_address (ElfParser     *parser,
 gboolean      elf_parser_owns_symbol     (ElfParser     *parser,
 					  const ElfSym  *sym);
 char *        elf_demangle               (const char    *name);
-