Basic when statement - Compile time if statement

This is similar to an #if in C but handled during the semantic checking stage.

code/demo.odin

@@ -1,11 +1,27 @@
-#import "fmt.odin"
+// #import "fmt.odin"
 #import "utf8.odin"
 
+when ODIN_OS == "window" {
+	when ODIN_OS != "window" {
+	} else {
+		MAX :: 64
+	}
+	#import "fmt.odin"
+} else {
+
+}
+
+
 main :: proc() {
-	MAX :: 64
+	when true {
+		OffsetType :: type int
+	}
+
+	// MAX :: 64
 	buf:     [MAX]rune
 	backing: [MAX]byte
-	offset:  int
+	offset:  OffsetType
+
 
 	msg := "Hello"
 	count := utf8.rune_count(msg)
@@ -17,16 +33,17 @@ main :: proc() {
 		s := msg[offset:]
 		r, len := utf8.decode_rune(s)
 		runes[count-i-1] = r
-		offset += len
+		offset += len as OffsetType
 	}
 
 	offset = 0
 	for i := 0; i < count; i++ {
 		data, len := utf8.encode_rune(runes[i])
 		copy(backing[offset:], data[:len])
-		offset += len
+		offset += len as OffsetType
 	}
 
 	reverse := backing[:offset] as string
 	fmt.println(reverse) // olleH
 }
+