shaderir: Bug fix: Wrong function names for some bulitin funcs

internal/shaderir/glsl.go

@@ -307,7 +307,7 @@ func (p *Program) glslBlock(topBlock, block *Block, level int, localVarIndex int
 		case StructMember:
 			return fmt.Sprintf("M%d", e.Index)
 		case BuiltinFuncExpr:
-			return string(e.BuiltinFunc)
+			return e.BuiltinFunc.Glsl()
 		case SwizzlingExpr:
 			if !isValidSwizzling(e.Swizzling) {
 				return fmt.Sprintf("?(unexpected swizzling: %s)", e.Swizzling)

internal/shaderir/program.go

@@ -307,3 +307,20 @@ func ParseBuiltinFunc(str string) (BuiltinFunc, bool) {
 	}
 	return "", false
 }
+
+func (f BuiltinFunc) Glsl() string {
+	switch f {
+	case LessThan:
+		return "lessThan"
+	case LessThanEqual:
+		return "lessThanEqual"
+	case GreaterThan:
+		return "greaterThan"
+	case GreaterThanEqual:
+		return "greaterThanEqual"
+	case NotEqual:
+		return "notEqual"
+	default:
+		return string(f)
+	}
+}