w6l: link GNU long-name archive members; bad members fail the link

The archive walk skipped every member whose header name starts
with '/', which also dropped GNU long-name members (/N) -- any
member with a >15-char filename silently never linked. Only '/ '
(symbol index) and '//' (long-name table) are non-objects; /N
members index by content (names are never consulted). A member
that fails loadimage in the selective pull also stayed silently
unlinked with rc=0; it now reports and fails the link (rule 7).
wwstage w6l diagnostics ride the same .len idiom as the w6a sweep.

selfhost/cmd/w6l/dyn.ww

@@ -168,11 +168,13 @@ export fn loadso(l: *lnk, path: *u8) i32 = {
 	let blen: u64;
 	buf, blen = slurpso(path);
 	if (buf == nil) {
-		os.write(2, "w6l: cannot read .so\n".ptr, 20u64);
+		let wm1: str = "w6l: cannot read .so\n";
+		os.write(2, wm1.ptr, wm1.len: u64);
 		return -1;
 	};
 	if (blen < 64u64) {
-		os.write(2, "w6l: short ELF\n".ptr, 14u64);
+		let wm2: str = "w6l: short ELF\n";
+		os.write(2, wm2.ptr, wm2.len: u64);
 		return -1;
 	};
 	if (buf[0u64] != 127u8) { return soerr("not ELF"); };
@@ -349,9 +351,11 @@ export fn loadso(l: *lnk, path: *u8) i32 = {
 };
 
 fn soerr(msg: str) i32 = {
-	os.write(2, "w6l: ".ptr, 4u64);
+	let wm3: str = "w6l: ";
+	os.write(2, wm3.ptr, wm3.len: u64);
 	os.write(2, msg.ptr, msg.len: u64);
-	os.write(2, "\n".ptr, 1u64);
+	let wm4: str = "\n";
+	os.write(2, wm4.ptr, wm4.len: u64);
 	return -1;
 };