HostCross is an attribute of a Target, not OsType

A host target is considered as being cross-compiled when the target
can't run natively on the build machine. For example, linux_glibc/x86_64
is a non-cross target on a standard x86/Linux machine, but is a cross
host on Mac. Previously, whether cross or not was a static attribute of
an OsType. For example, Windows was always considered as cross host,
while linux_bionic was not. This becomes a problem when we support more
host targets like linux_bionic/arm64 which should be cross-host on
standard x86/Linux machines.

This change removes HostCross from the OsClass type and instead adds a
property HostCross to the Target type. When a target is being added, it
is initialized to true when the target can't run natively on the current
build machine.

Bug: 168086242
Test: m
Change-Id: Ic37c8db918873ddf324c86b12b5412952b0f2be2
diff --git a/cc/cc.go b/cc/cc.go
index 6584380..d0d6427 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -950,9 +950,9 @@
 		c.AddProperties(feature.props()...)
 	}
 
-	c.Prefer32(func(ctx android.BaseModuleContext, base *android.ModuleBase, class android.OsClass) bool {
+	c.Prefer32(func(ctx android.BaseModuleContext, base *android.ModuleBase, os android.OsType) bool {
 		// Windows builds always prefer 32-bit
-		return class == android.HostCross
+		return os == android.Windows
 	})
 	android.InitAndroidArchModule(c, c.hod, c.multilib)
 	android.InitApexModule(c)