checker: c2v fixes

vlib/builtin/cfns.c.v

@@ -171,6 +171,9 @@ fn C.tolower(c int) int
 [trusted]
 fn C.toupper(c int) int
 
+[trusted]
+fn C.strchr(s &char, c int) &char
+
 [trusted]
 fn C.getchar() int
 

vlib/v/checker/checker.v

@@ -2704,7 +2704,8 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 				}
 			}
 		}
-	} else if to_type == ast.bool_type && from_type != ast.bool_type && !c.inside_unsafe {
+	} else if to_type == ast.bool_type && from_type != ast.bool_type && !c.inside_unsafe
+		&& !c.pref.translated {
 		c.error('cannot cast to bool - use e.g. `some_int != 0` instead', node.pos)
 	} else if from_type == ast.none_type && !to_type.has_flag(.optional) {
 		type_name := c.table.type_to_str(to_type)

vlib/v/checker/if.v

@@ -28,7 +28,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 	mut is_comptime_type_is_expr := false // if `$if T is string`
 	for i in 0 .. node.branches.len {
 		mut branch := node.branches[i]
-		if branch.cond is ast.ParExpr {
+		if branch.cond is ast.ParExpr && !c.pref.translated {
 			c.error('unnecessary `()` in `$if_kind` condition, use `$if_kind expr {` instead of `$if_kind (expr) {`.',
 				branch.pos)
 		}

vlib/v/checker/match.v

@@ -8,7 +8,7 @@ import strings
 pub fn (mut c Checker) match_expr(mut node ast.MatchExpr) ast.Type {
 	node.is_expr = c.expected_type != ast.void_type
 	node.expected_type = c.expected_type
-	if node.cond is ast.ParExpr {
+	if node.cond is ast.ParExpr && !c.pref.translated {
 		c.error('unnecessary `()` in `match` condition, use `match expr {` instead of `match (expr) {`.',
 			node.cond.pos)
 	}