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/android/config.go b/android/config.go
index 1c06e8c..f8c8821 100644
--- a/android/config.go
+++ b/android/config.go
@@ -260,10 +260,10 @@
 	config := testConfig.config
 
 	config.Targets[Android] = []Target{
-		{Android, Arch{ArchType: X86_64, ArchVariant: "silvermont", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", ""},
-		{Android, Arch{ArchType: X86, ArchVariant: "silvermont", Abi: []string{"armeabi-v7a"}}, NativeBridgeDisabled, "", ""},
-		{Android, Arch{ArchType: Arm64, ArchVariant: "armv8-a", Abi: []string{"arm64-v8a"}}, NativeBridgeEnabled, "x86_64", "arm64"},
-		{Android, Arch{ArchType: Arm, ArchVariant: "armv7-a-neon", Abi: []string{"armeabi-v7a"}}, NativeBridgeEnabled, "x86", "arm"},
+		{Android, Arch{ArchType: X86_64, ArchVariant: "silvermont", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", "", false},
+		{Android, Arch{ArchType: X86, ArchVariant: "silvermont", Abi: []string{"armeabi-v7a"}}, NativeBridgeDisabled, "", "", false},
+		{Android, Arch{ArchType: Arm64, ArchVariant: "armv8-a", Abi: []string{"arm64-v8a"}}, NativeBridgeEnabled, "x86_64", "arm64", false},
+		{Android, Arch{ArchType: Arm, ArchVariant: "armv7-a-neon", Abi: []string{"armeabi-v7a"}}, NativeBridgeEnabled, "x86", "arm", false},
 	}
 
 	return testConfig
@@ -275,10 +275,10 @@
 
 	config.Targets = map[OsType][]Target{
 		Fuchsia: []Target{
-			{Fuchsia, Arch{ArchType: Arm64, ArchVariant: "", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", ""},
+			{Fuchsia, Arch{ArchType: Arm64, ArchVariant: "", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", "", false},
 		},
 		BuildOs: []Target{
-			{BuildOs, Arch{ArchType: X86_64}, NativeBridgeDisabled, "", ""},
+			{BuildOs, Arch{ArchType: X86_64}, NativeBridgeDisabled, "", "", false},
 		},
 	}
 
@@ -292,12 +292,12 @@
 
 	config.Targets = map[OsType][]Target{
 		Android: []Target{
-			{Android, Arch{ArchType: Arm64, ArchVariant: "armv8-a", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", ""},
-			{Android, Arch{ArchType: Arm, ArchVariant: "armv7-a-neon", Abi: []string{"armeabi-v7a"}}, NativeBridgeDisabled, "", ""},
+			{Android, Arch{ArchType: Arm64, ArchVariant: "armv8-a", Abi: []string{"arm64-v8a"}}, NativeBridgeDisabled, "", "", false},
+			{Android, Arch{ArchType: Arm, ArchVariant: "armv7-a-neon", Abi: []string{"armeabi-v7a"}}, NativeBridgeDisabled, "", "", false},
 		},
 		BuildOs: []Target{
-			{BuildOs, Arch{ArchType: X86_64}, NativeBridgeDisabled, "", ""},
-			{BuildOs, Arch{ArchType: X86}, NativeBridgeDisabled, "", ""},
+			{BuildOs, Arch{ArchType: X86_64}, NativeBridgeDisabled, "", "", false},
+			{BuildOs, Arch{ArchType: X86}, NativeBridgeDisabled, "", "", false},
 		},
 	}