w6l: purge dead elf branches; pin rx extent

selfhost/cmd/w6l/out.ww

@@ -111,6 +111,8 @@ export fn emitelf(l: *lnk, fd: i32, base: u64, entry: u64) i32 = {
 	wru64(hdr.ptr, 80u64, base);		// p_vaddr
 	wru64(hdr.ptr, 88u64, base);		// p_paddr
 	wru64(hdr.ptr, 96u64, rxend);		// p_filesz
+	// The loader page-rounds mappings; when present, dataoff starts
+	// independently on the next page, so padding is not R+X extent.
 	wru64(hdr.ptr, 104u64, rxend);		// p_memsz
 	wru64(hdr.ptr, 112u64, TEXT_OFF);		// p_align