lint: replace switch statement in dcs_merge_declaration_specifiers

Grouping the rules by their abstract type took a lot of visual space.
Instead, move each of the rules from C11 6.7.2 into its own if
statement, so that the rules almost read like in the standard.

No functional change.

usr.bin/xlint/lint1/decl.c

@@ -1,4 +1,4 @@
-/* $NetBSD: decl.c,v 1.204 2021/07/15 23:07:05 rillig Exp $ */
+/* $NetBSD: decl.c,v 1.205 2021/07/15 23:42:49 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -38,7 +38,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: decl.c,v 1.204 2021/07/15 23:07:05 rillig Exp $");
+__RCSID("$NetBSD: decl.c,v 1.205 2021/07/15 23:42:49 rillig Exp $");
 #endif
 
 #include <sys/param.h>
@@ -746,7 +746,11 @@ dcs_adjust_storage_class(void)
 	}
 }
 
-/* Merge the declaration specifiers from dcs into dcs->d_type. */
+/*
+ * Merge the declaration specifiers from dcs into dcs->d_type.
+ *
+ * See C99 6.7.2 "Type specifiers".
+ */
 static void
 dcs_merge_declaration_specifiers(void)
 {
@@ -776,55 +780,34 @@ dcs_merge_declaration_specifiers(void)
 		return;
 	}
 
-	switch (t) {
-	case BOOL:
-		break;
-	case NOTSPEC:
+	if (t == NOTSPEC)
 		t = INT;
-		/* FALLTHROUGH */
-	case INT:
-		if (s == NOTSPEC)
-			s = SIGNED;
-		break;
-	case CHAR:
-		if (l != NOTSPEC) {
-			dcs->d_terr = true;
-			l = NOTSPEC;
-		}
-		break;
-	case FLOAT:
-		if (l == LONG) {
-			l = NOTSPEC;
-			t = DOUBLE;
-			if (!tflag)
-				/* use 'double' instead of 'long float' */
-				warning(6);
-		}
-		break;
-	case DOUBLE:
-		if (l != LONG)
-			break;
-		/* FALLTHROUGH */
-	case LDOUBLE:
+	if (s == NOTSPEC && t == INT)
+		s = SIGNED;
+	if (l != NOTSPEC && t == CHAR) {
+		dcs->d_terr = true;
+		l = NOTSPEC;
+	}
+	if (l == LONG && t == FLOAT) {
+		l = NOTSPEC;
+		t = DOUBLE;
+		if (!tflag)
+			/* use 'double' instead of 'long float' */
+			warning(6);
+	}
+	if ((l == LONG && t == DOUBLE) || t == LDOUBLE) {
 		l = NOTSPEC;
 		t = LDOUBLE;
-		if (tflag)
-			/* 'long double' is illegal in traditional C */
-			warning(266);
-		break;
-	case DCOMPLEX:
-		if (l == LONG) {
-			l = NOTSPEC;
-			t = LCOMPLEX;
-		}
-		break;
-	case VOID:
-	case FCOMPLEX:
-	case LCOMPLEX:
-		break;
-	default:
-		lint_assert(is_integer(t));
 	}
+	if (t == LDOUBLE && tflag) {
+		/* 'long double' is illegal in traditional C */
+		warning(266);
+	}
+	if (l == LONG && t == DCOMPLEX) {
+		l = NOTSPEC;
+		t = LCOMPLEX;
+	}
+
 	if (t != INT && t != CHAR && (s != NOTSPEC || l != NOTSPEC)) {
 		dcs->d_terr = true;
 		l = s = NOTSPEC;