MINOR: tools: add get_exec_path implementation for solaris based systems.

We can use getexecname() which fetches AT_SUN_EXECNAME from the auxiliary
vectors.

(cherry picked from commit 7198c700bc1881c115062d9a4019b960ab0e0b57)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 684e4b12ae5f7d88b3b7f8437f55fcf0eebb1cf5)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/tools.c b/src/tools.c
index bbd6a76..52b4890 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -4796,6 +4796,8 @@
 			break;
 		}
 	}
+#elif defined(__sun)
+	ret = getexecname();
 #endif
 	return ret;
 }