cmd/gc: remove mentions of "ideal" from error messages.

        _ = complex("foo", 0)
        _ = complex(true, 0)
now trigger:
        x.go:4: invalid operation: complex("foo", 0) (mismatched types untyped string and untyped number)
        x.go:5: invalid operation: complex(true, 0) (mismatched types untyped bool and untyped number)

Fixes #4521

R=golang-dev, remyoudompheng, rsc
CC=golang-dev
https://golang.org/cl/12973043

src/cmd/gc/const.c

@@ -1056,7 +1056,7 @@ nodcplxlit(Val r, Val i)
 }
 
 // idealkind returns a constant kind like consttype
-// but for an arbitrary "ideal" expression.
+// but for an arbitrary "ideal" (untyped constant) expression.
 static int
 idealkind(Node *n)
 {

src/cmd/gc/fmt.c

@@ -577,7 +577,7 @@ basicnames[] =
 	[TANY]		= "any",
 	[TSTRING]	= "string",
 	[TNIL]		= "nil",
-	[TIDEAL]	= "ideal",
+	[TIDEAL]	= "untyped number",
 	[TBLANK]	= "blank",
 };
 
@@ -619,7 +619,7 @@ typefmt(Fmt *fp, Type *t)
 
 	if(t->etype < nelem(basicnames) && basicnames[t->etype] != nil) {
 		if(fmtmode == FErr && (t == idealbool || t == idealstring))
-			fmtstrcpy(fp, "ideal ");
+			fmtstrcpy(fp, "untyped ");
 		return fmtstrcpy(fp, basicnames[t->etype]);
 	}
 

src/cmd/gc/typecheck.c

@@ -90,7 +90,7 @@ static char* _typekind[] = {
 	[TARRAY]	= "array",
 	[TFUNC]		= "func",
 	[TNIL]		= "nil",
-	[TIDEAL]	= "ideal number",
+	[TIDEAL]	= "untyped number",
 };
 
 static char*