wcc/ww: global-str default-hi slice arg loads its len word

Slicing a module-global str with default hi emitted nothing for the
bound; load the len word from g(SB)+8 (mirror the cstage twin).
Review item #47; dual-stage rows red-proven.

selfhost/cmd/wcc/cgenutil.ww

@@ -620,7 +620,14 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node, memphase: bool) i32 = {
 				emitsymname(c, globalname);
 				emitline("(SB), CX\n");
 				emitline("\tMOVQ\t8(CX), AX\n");
-			};};
+			} else { if (globaltn.kind == nkind.N_TNAME) {
+				if (streq(globaltn.str, "str")) {
+					emitline("\tLEAQ\t");
+					emitsymname(c, globalname);
+					emitline("(SB), CX\n");
+					emitline("\tMOVQ\t8(CX), AX\n");
+				};
+			};};};
 			// #60: alias-NAMED global base default-hi — chased
 			// kind; runtime-unreachable until #77/#78 global DATA.
 			if (bu60 != nil) {