checker: improve virtual C consts

vlib/net/address_darwin.c.v

@@ -34,6 +34,8 @@ mut:
 	sin_zero   [8]char
 }
 
+const C.AF_INET u8
+
 pub struct C.sockaddr_un {
 mut:
 	sun_len    u8

vlib/v/checker/checker.v

@@ -4297,8 +4297,7 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 		if node.name == 'C.NULL' {
 			return ast.voidptr_type
 		}
-		// TODO remove main. to avoid extra concats
-		if x := c.table.global_scope.find_const('main.' + node.name) {
+		if x := c.table.global_scope.find_const(node.name) {
 			return x.typ
 		}
 		return ast.int_type

vlib/v/gen/c/consts_and_globals.v

@@ -309,6 +309,9 @@ fn (mut g Gen) c_const_name(name string) string {
 }
 
 fn (mut g Gen) const_decl_init_later(mod string, name string, expr ast.Expr, typ ast.Type, surround_cbr bool) {
+	if name.starts_with('C__') {
+		return
+	}
 	// Initialize more complex consts in `void _vinit/2{}`
 	// (C doesn't allow init expressions that can't be resolved at compile time).
 	mut styp := g.styp(typ)

vlib/v/parser/parser.v

@@ -2384,7 +2384,7 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 			p.error_with_pos('const names cannot contain uppercase letters, use snake_case instead',
 				pos)
 		}
-		full_name := p.prepend_mod(name)
+		full_name := if is_virtual_c_const { name } else { p.prepend_mod(name) }
 		if p.tok.kind == .comma {
 			p.error_with_pos('const declaration do not support multiple assign yet', p.tok.pos())
 		}

vlib/v/tests/c_const_u8_test.v

@@ -1,9 +1,17 @@
-const C.AF_INET u16
+import net
 
-fn x(n u16) bool {
+const C.AF_UNIX u16
+
+fn x16(n u16) bool {
+	return true
+}
+
+fn xint(n int) bool {
 	return true
 }
 
 fn test_const() {
-	assert x(C.AF_INET) == true
+	assert xint(C.EOF) == true // a random libc const is int by default
+
+	assert x16(C.AF_INET) == true // defined in V's net module
 }