add noreturn and unreachable

compiler/types/types.odin

@@ -45,6 +45,7 @@ FLOAT :: Type(30)
 RANGE :: Type(31)
 ANYOPAQUE :: Type(32)
 UINT :: Type(33)
+NORETURN :: Type(34)
 
 DYNAMIC_START :: Type(64)
 
@@ -58,6 +59,7 @@ Numeric_Category :: enum u8 {
 Kind :: enum u8 {
 	Invalid,
 	Void,
+	Noreturn,
 	Anyopaque,
 	Int_Constraint,
 	Uint_Constraint,
@@ -599,6 +601,8 @@ kind :: proc(value: Type, store: ^Store = nil) -> Kind {
 		return .Invalid
 	case VOID:
 		return .Void
+	case NORETURN:
+		return .Noreturn
 	case ANYOPAQUE:
 		return .Anyopaque
 	case INT:
@@ -643,6 +647,10 @@ is_void :: proc(value: Type) -> bool {
 	return value == VOID
 }
 
+is_noreturn :: proc(value: Type) -> bool {
+	return value == NORETURN
+}
+
 is_anyopaque :: proc(value: Type) -> bool {
 	return value == ANYOPAQUE
 }
@@ -1717,6 +1725,12 @@ can_coerce_c_scalar :: proc(from, to: Type, selected := target.DEFAULT) -> bool
 }
 
 widest :: proc(a, b: Type) -> Type {
+	if is_noreturn(a) {
+		return b
+	}
+	if is_noreturn(b) {
+		return a
+	}
 	if equal(a, b) && is_concrete_scalar(a) {
 		return a
 	}
@@ -1759,6 +1773,7 @@ name :: proc(value: Type) -> string {
 	switch value {
 	case INVALID:       return "<invalid>"
 	case VOID:          return "void"
+	case NORETURN:      return "noreturn"
 	case ANYOPAQUE:     return "anyopaque"
 	case BOOL:          return "bool"
 	case INT:           return "int"