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/python/binary.go b/python/binary.go
index 5a74926..1d2400e 100644
--- a/python/binary.go
+++ b/python/binary.go
@@ -79,7 +79,7 @@
 }
 
 func PythonBinaryHostFactory() android.Module {
-	module, _ := NewBinary(android.HostSupportedNoCross)
+	module, _ := NewBinary(android.HostSupported)
 
 	return module.Init()
 }