w6c,ww: mangle an imported package's fn main under separate compilation (M4 E3, #99)

The bare-`main` carve-out (which keeps the link entry's main unmangled)
keyed on `leaf == "main" && imported == 0`. Under the combined path a
dependency's body folds in with imported==1, so only the root's main
stayed bare. Under separate compilation each package is its own unit and
a dependency's body carries a path-mangling module-reset but imported==0
(#57) — so an imported `fn main` matched the carve-out, emitted a bare
`TEXT main`, and collided with the root entry (`w6l: duplicate symbol
main`). The combined path was unaffected, so this only surfaced under sep.

Gate the carve-out with sep_isdep = (wwiout != NULL): the producer emits a
.wwi output only for dependency units, never for the root/link-entry unit
(root stripped, #69), symmetric on both stages. Only the root unit's main
now stays bare; an imported package's main mangles on its import path
(e.g. aa.bb.main). Both stages.

Gate: test/wcc/989_depmain_sep.c (table-driven, dotted + single-component
shapes, both stages; asserts the mangled dep main + a single bare root
main + cs==ww byte-id; combined path stays neutral).

cmd/w6c/cgen.c

@@ -1477,8 +1477,14 @@ mod_collect(Cg *c, Node *file)
 		 * primary's decls are MODULED "main", so main is NOT bare here;
 		 * skip it (cgfn force-emits the bare `main` label). M1 #32: only
 		 * the ROOT main (imported==0) stays bare; an IMPORTED `fn main`
-		 * mangles on its path (closes #31's dup-main by construction). */
-		if (d->str && strcmp(d->str, "main") == 0 && !d->imported)
+		 * mangles on its path (closes #31's dup-main by construction).
+		 * #99: under sep a dep unit's main is imported==0 too (its body
+		 * is composed with a path-carrying `//ww:module-reset`, #57), so
+		 * imported==0 no longer means "root unit" per-unit. Gate on
+		 * !sep_isdep (wwiout==NULL <=> root/link-entry unit, #69) so only
+		 * the root's main stays bare; a dep's main mangles on its path. */
+		if (d->str && strcmp(d->str, "main") == 0 && !d->imported
+		    && !c->sep_isdep)
 			continue;
 		Mod *m = amalloc(c->a, sizeof *m);
 		m->name = d->str;
@@ -14960,8 +14966,12 @@ cgfn(Cg *c, FILE *out, Node *fn)
 	 * NOT a bare-module decl — removing this carve-out mangles it to
 	 * `main.main` (undefined `main`). #84's bare-module handling is the
 	 * orthogonal axis (a package-LESS `//ww:module-reset` fn, cur_mod
-	 * NULL), resolved in mod_lookup_for_fn, NOT here. */
-	if (fn->str && strcmp(fn->str, "main") == 0 && !fn->imported)
+	 * NULL), resolved in mod_lookup_for_fn, NOT here. #99: gate on
+	 * !sep_isdep — under sep a dep unit's main is imported==0 (path-
+	 * carrying `//ww:module-reset`, #57); only the root/link-entry unit
+	 * (wwiout==NULL, #69) keeps the bare label. */
+	if (fn->str && strcmp(fn->str, "main") == 0 && !fn->imported
+	    && !c->sep_isdep)
 		text->to = asym("main");
 	else
 		text->to = mafn(c, fn->str, c->cur_mod);

cmd/w6c/gc.h

@@ -54,6 +54,14 @@ struct Cg {
 				 * the dep's real definition (link collision).
 				 * Off on the combined path (every existing
 				 * invocation) so M3 is a pure addition. */
+	int	sep_isdep;	/* #99: this unit is a sep DEPENDENCY, not the
+				 * root/link-entry unit. Set from `wwiout != NULL`
+				 * in main: the producer passes -I (.wwi output)
+				 * to DEP units only — the root's .wwi is stripped
+				 * (#69), so wwiout==NULL <=> root/link-entry unit.
+				 * Gates the bare-`main` carve-out: a dep's `fn
+				 * main` must mangle on its path like any decl;
+				 * only the root entry stays bare. */
 };
 
 /* cgen.c */

cmd/w6c/main.c

@@ -110,6 +110,10 @@ main(int argc, char **argv)
 
 	cg_init(&cg, a);
 	cg.sep_mode = sepmode;
+	/* #99: wwiout != NULL <=> this is a sep DEP unit (the producer passes
+	 * -I to deps only; the root's .wwi is stripped per #69). Gates the
+	 * bare-`main` carve-out so only the root/link-entry main stays bare. */
+	cg.sep_isdep = (wwiout != NULL);
 	cg_file(&cg, of, file);
 
 	if (of != stdout) fclose(of);