Don't check for RELRO on MorphOS

It's not supported, but accepted by the toolchain, which will just issue
a warning.

FossilOrigin-Name: 0f70ee1915bb453293eeed9c511ca6ddd72271782b1a562c8138a56e1ba01ed9

build-aux/m4/buildsys.m4

@@ -323,9 +323,13 @@ AC_DEFUN([BUILDSYS_RELRO], [
 	AC_REQUIRE([AC_CANONICAL_HOST])
 	AC_MSG_CHECKING(for RELRO support)
 
+	case "$host_os" in
+	morphos*)
+		AC_MSG_RESULT(no)
+		;;
+	*)
 		old_LDFLAGS="$LDFLAGS"
 		LDFLAGS="$LDFLAGS -Wl,-z,relro,-z,now"
-
 		AC_LINK_IFELSE([
 			AC_LANG_PROGRAM([
 				#include <stdio.h>
@@ -340,6 +344,8 @@ AC_DEFUN([BUILDSYS_RELRO], [
 		])
 
 		LDFLAGS="$old_LDFLAGS"
+		;;
+	esac
 ])
 
 AC_DEFUN([BUILDSYS_SHARED_LIB], [