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/pass.ww

@@ -56,10 +56,12 @@ export fn resolve(l: *lnk) i32 = {
 		if (r2.sym != nil) {
 			if (r2.sym.defined == 0) {
 				if (r2.sym.isdyn == 0) {
-					os.write(2, "w6l: undefined reference to '".ptr, 28u64);
+					let wm1: str = "w6l: undefined reference to '";
+					os.write(2, wm1.ptr, wm1.len: u64);
 					let nm: str = r2.sym.name;
 					os.write(2, nm.ptr, nm.len: u64);
-					os.write(2, "'\n".ptr, 2u64);
+					let wm2: str = "'\n";
+					os.write(2, wm2.ptr, wm2.len: u64);
 					l.errs += 1;
 				};
 			};
@@ -113,7 +115,8 @@ export fn relocate(l: *lnk, textva: u64, datava: u64) i32 = {
 						patchu64(l.text + r.off, v);
 					};
 				case:
-					os.write(2, "w6l: unsupported reloc kind\n".ptr, 27u64);
+					let wm3: str = "w6l: unsupported reloc kind\n";
+					os.write(2, wm3.ptr, wm3.len: u64);
 					l.errs += 1;
 				};
 			};