Use proptools.BoolDefault

Replace x == nil || *x with proptools.BoolDefault(x, true)

Test: m checkbuild
Change-Id: Icc5378cab3ea72d86544b40761c2f00b278cc0a1
diff --git a/cc/cc.go b/cc/cc.go
index c8d5251..ce1cb0a 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -1585,6 +1585,7 @@
 }
 
 var Bool = proptools.Bool
+var BoolDefault = proptools.BoolDefault
 var BoolPtr = proptools.BoolPtr
 var String = proptools.String
 var StringPtr = proptools.StringPtr