ldd: Use __PATH_RTLD("32") over _COMPAT32_PATH_RTLD

This will allow the latter to be removed, reducing the boilerplate
needed for a new libcompat.

Reviewed by:	kib, brooks, jhb
Differential Revision:	https://reviews.freebsd.org/D40934

usr.bin/ldd/ldd.c

@@ -236,7 +236,7 @@ main(int argc, char *argv[])
 			rtld = _PATH_RTLD;
 #if __ELF_WORD_SIZE > 32 && defined(ELF32_SUPPORTED)
 			if (type == TYPE_ELF32)
-				rtld = _COMPAT32_PATH_RTLD;
+				rtld = __PATH_RTLD("32");
 #endif
 			if (is_shlib == 0) {
 				execl(rtld, rtld, "--",