BUILD: tools: make resolve_sym_name() return a const

Originally it was made to return a void* because some comparisons in the
code where it was used required a lot of casts. But now we don't need
that anymore. And having it non-const breaks the build on NetBSD 9 as
reported in issue #728.

So let's switch to const and adjust debug.c to accomodate this.

include/haproxy/tools.h

@@ -996,7 +996,7 @@ int dump_text_line(struct buffer *out, const char *buf, int bsize, int len,
 void dump_addr_and_bytes(struct buffer *buf, const char *pfx, const void *addr, int n);
 void dump_hex(struct buffer *out, const char *pfx, const void *buf, int len, int unsafe);
 int may_access(const void *ptr);
-void *resolve_sym_name(struct buffer *buf, const char *pfx, void *addr);
+const void *resolve_sym_name(struct buffer *buf, const char *pfx, void *addr);
 const char *get_exec_path();
 
 #if defined(USE_BACKTRACE)

src/debug.c

@@ -98,7 +98,7 @@ void ha_thread_dump(struct buffer *buf, int thr, int calling_tid)
 		struct buffer bak;
 		void *callers[100];
 		int j, nptrs;
-		void *addr;
+		const void *addr;
 		int dump = 0;
 
 		nptrs = my_backtrace(callers, sizeof(callers)/sizeof(*callers));

src/tools.c

@@ -4426,7 +4426,7 @@ static int dladdr_and_size(const void *addr, Dl_info *dli, size_t *size)
  * The symbol's base address is returned, or NULL when unresolved, in order to
  * allow the caller to match it against known ones.
  */
-void *resolve_sym_name(struct buffer *buf, const char *pfx, void *addr)
+const void *resolve_sym_name(struct buffer *buf, const char *pfx, void *addr)
 {
 	const struct {
 		const void *func;