Prebuilt_etc can be uninstallable

For APEXs, we need different prebuilt_etc modules having the same
'filename' properties, because we expect them to have same local path
inside APEXs. For example, we will have ./etc/ld.config.txt file for
APEXs having an executable.

However, this can cause duplicated targets in the make world, because
the prebuilt_etc modules will all be installed to the same path under
/system.

In order to avoid this, adding 'installable' property to prebuilt_etc
module type to optionally make a module to be non-installable, but only
to APEXs.

Test: build/soong/build_test.bash --dist

Change-Id: Iadb564e07d0483934548ca63f5f524a2c8515a81
diff --git a/android/prebuilt_etc.go b/android/prebuilt_etc.go
index cc1f846..83c38db 100644
--- a/android/prebuilt_etc.go
+++ b/android/prebuilt_etc.go
@@ -44,6 +44,9 @@
 	Recovery_available *bool
 
 	InRecovery bool `blueprint:"mutated"`
+
+	// Whether this module is directly installable to one of the partitions. Default: true.
+	Installable *bool
 }
 
 type PrebuiltEtc struct {
@@ -96,6 +99,10 @@
 	return String(p.properties.Sub_dir)
 }
 
+func (p *PrebuiltEtc) Installable() bool {
+	return p.properties.Installable == nil || Bool(p.properties.Installable)
+}
+
 func (p *PrebuiltEtc) GenerateAndroidBuildActions(ctx ModuleContext) {
 	p.sourceFilePath = ctx.ExpandSource(String(p.properties.Src), "src")
 	filename := String(p.properties.Filename)
@@ -128,6 +135,7 @@
 			fmt.Fprintln(w, "LOCAL_PREBUILT_MODULE_FILE :=", p.outputFilePath.String())
 			fmt.Fprintln(w, "LOCAL_MODULE_PATH :=", "$(OUT_DIR)/"+p.installDirPath.RelPathString())
 			fmt.Fprintln(w, "LOCAL_INSTALLED_MODULE_STEM :=", p.outputFilePath.Base())
+			fmt.Fprintln(w, "LOCAL_UNINSTALLABLE_MODULE :=", !p.Installable())
 			if p.additionalDependencies != nil {
 				fmt.Fprint(w, "LOCAL_ADDITIONAL_DEPENDENCIES :=")
 				for _, path := range *p.additionalDependencies {