Add ApexModule interface for APEX-aware modules

ApexModule is the interface for APEX-aware modules. The module type apex
uses the interface to get APEX-specific information from other modules,
such as the list of APEXs that a module should be built for.

A module that is included in an APEX will be built specificaly for the
APEX. This is especially required for shared libraries; we shouldn't
just copy the artifacts built for platform, because they may be linking
against private (=unstable) symbols that are not available to APEXs
which are basically unbundled.

This CL, as a first step, makes cc.Module an APEX-aware module type.

Bug: 112672359
Test: m apex.test; the built apex has all the direct and transitive
shared lib dependencies of the libs and executables listed in Android.bp

Change-Id: I21f6a586654779984f0f5154b2a08b2adbf2168b
diff --git a/cc/cc.go b/cc/cc.go
index 5f3baea..6320b9c 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -320,6 +320,7 @@
 type Module struct {
 	android.ModuleBase
 	android.DefaultableModuleBase
+	android.ApexModuleBase
 
 	Properties       BaseProperties
 	VendorProperties VendorProperties
@@ -416,6 +417,8 @@
 
 	android.InitDefaultableModule(c)
 
+	android.InitApexModule(c)
+
 	return c
 }
 
@@ -794,7 +797,7 @@
 		c.outputFile = android.OptionalPathForPath(outputFile)
 	}
 
-	if c.installer != nil && !c.Properties.PreventInstall && c.outputFile.Valid() {
+	if c.installer != nil && !c.Properties.PreventInstall && c.IsForPlatform() && c.outputFile.Valid() {
 		c.installer.install(ctx, c.outputFile.Path())
 		if ctx.Failed() {
 			return
@@ -1511,12 +1514,24 @@
 	}
 }
 
+// Overrides ApexModule.IsInstallabeToApex()
+// Only shared libraries are installable to APEX.
+func (c *Module) IsInstallableToApex() bool {
+	if shared, ok := c.linker.(interface {
+		shared() bool
+	}); ok {
+		return shared.shared()
+	}
+	return false
+}
+
 //
 // Defaults
 //
 type Defaults struct {
 	android.ModuleBase
 	android.DefaultsModuleBase
+	android.ApexModuleBase
 }
 
 func (*Defaults) GenerateAndroidBuildActions(ctx android.ModuleContext) {
@@ -1558,6 +1573,7 @@
 	)
 
 	android.InitDefaultsModule(module)
+	android.InitApexModule(module)
 
 	return module
 }