Install VNDK snapshot libraries for system build

When BOARD_VNDK_VERSION := <VNDK version>, or
PRODUCT_EXTRA_VNDK_VERSIONS includes the needed <VNDK version> list,
the prebuilt VNDK libs in prebuilts/vndk/ directory will be
installed.

Each prebuilt VNDK module uses "vndk_prebuilt_shared" for shared
VNDK/VNDK-SP libs.

Following is the sample configuration of a vndk snapshot module:
vndk_prebuilt_shared {
    name: "libfoo",
    version: "27",
    vendor_available: true,
    vndk: {
        enabled: true,
    },
    arch: {
        arm64: {
            srcs: ["arm/lib64/libfoo.so"],
        },
        arm: {
            srcs: ["arm/lib/libfoo.so"],
        },
    },
}

The Android.bp for the snapshot modules will be auto-generated by a
script.

Bug: 38304393
Bug: 65377115
Bug: 68123344
Test: set BOARD_VNDK_VERSION := 27
      copy a snapshot for v27
      build with make command

Change-Id: Ib93107530dbabb4a24583f4d6e4f0c513c9adfec
diff --git a/cc/cc.go b/cc/cc.go
index 891dccb..c31cf04 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -1372,7 +1372,7 @@
 
 	if genrule, ok := mctx.Module().(*genrule.Module); ok {
 		if props, ok := genrule.Extra.(*VendorProperties); ok {
-			if !mctx.DeviceConfig().CompileVndk() {
+			if mctx.DeviceConfig().VndkVersion() == "" {
 				mctx.CreateVariations(coreMode)
 			} else if Bool(props.Vendor_available) {
 				mctx.CreateVariations(coreMode, vendorMode)
@@ -1408,7 +1408,7 @@
 		}
 	}
 
-	if !mctx.DeviceConfig().CompileVndk() {
+	if mctx.DeviceConfig().VndkVersion() == "" {
 		// If the device isn't compiling against the VNDK, we always
 		// use the core mode.
 		mctx.CreateVariations(coreMode)
@@ -1419,6 +1419,12 @@
 	} else if _, ok := m.linker.(*llndkHeadersDecorator); ok {
 		// ... and LL-NDK headers as well
 		mctx.CreateVariations(vendorMode)
+	} else if _, ok := m.linker.(*vndkPrebuiltLibraryDecorator); ok {
+		// Make vendor variants only for the versions in BOARD_VNDK_VERSION and
+		// PRODUCT_EXTRA_VNDK_VERSIONS.
+		mod := mctx.CreateVariations(vendorMode)
+		vendor := mod[0].(*Module)
+		vendor.Properties.UseVndk = true
 	} else if m.hasVendorVariant() {
 		// This will be available in both /system and /vendor
 		// or a /system directory that is available to vendor.