Add ctx.Windows()

Replace ctx.Os() == android.Windows with ctx.Windows()

Test: builds
Change-Id: I7c24c39bcf54a51ad152b21c0021e40a0c07f189
diff --git a/android/module.go b/android/module.go
index 4fba1cf..3c09b3e 100644
--- a/android/module.go
+++ b/android/module.go
@@ -57,6 +57,7 @@
 	Host() bool
 	Device() bool
 	Darwin() bool
+	Windows() bool
 	Debug() bool
 	PrimaryArch() bool
 	Proprietary() bool
@@ -611,6 +612,10 @@
 	return a.target.Os == Darwin
 }
 
+func (a *androidBaseContextImpl) Windows() bool {
+	return a.target.Os == Windows
+}
+
 func (a *androidBaseContextImpl) Debug() bool {
 	return a.debug
 }