Add install_in_root to cc_binary

To support init_first_stage, install_in_root property is added to
cc_binary. The output is installed to {partition}, rather than
{partition}/{mount_point}/bin.

Bug: 187196593
Test: build init_first_stage
Change-Id: Ibc351645308676ed188f748972eb6312c9cbd64f

cc/installer.go

@@ -25,6 +25,10 @@ import (
 type InstallerProperties struct {
 	// install to a subdirectory of the default install path for the module
 	Relative_install_path *string `android:"arch_variant"`
+
+	// Install output directly in {partition}/, not in any subdir.  This is only intended for use by
+	// init_first_stage.
+	Install_in_root *bool `android:"arch_variant"`
 }
 
 type installLocation int
@@ -66,6 +70,11 @@ func (installer *baseInstaller) installDir(ctx ModuleContext) android.InstallPat
 	if ctx.toolchain().Is64Bit() && installer.dir64 != "" {
 		dir = installer.dir64
 	}
+
+	if installer.installInRoot() {
+		dir = ""
+	}
+
 	if ctx.Target().NativeBridge == android.NativeBridgeEnabled {
 		dir = filepath.Join(dir, ctx.Target().NativeBridgeRelativePath)
 	} else if !ctx.Host() && ctx.Config().HasMultilibConflict(ctx.Arch().ArchType) {
@@ -110,3 +119,7 @@ func (installer *baseInstaller) relativeInstallPath() string {
 func (installer *baseInstaller) makeUninstallable(mod *Module) {
 	mod.ModuleBase.MakeUninstallable()
 }
+
+func (installer *baseInstaller) installInRoot() bool {
+	return Bool(installer.Properties.Install_in_root)
+}