Soong: Add synopsis to several modules under the cc package.

Added synopsis to the following modules under cc package:
    * llndk_headers
    * llndk_library
    * vendor_public_library
    * toolchain_library

Bug: b/128337482
Test: Generated the documentation and verified that the synopsis was
added to each of the module.

Change-Id: I0f6e3b01b478d46afeacbe6fc8e05f96d6217c7d

cc/llndk_library.go

@@ -189,6 +189,14 @@ func NewLLndkStubLibrary() *Module {
 	return module
 }
 
+// llndk_library creates a stub llndk shared library based on the provided
+// version file. Example:
+//
+//    llndk_library {
+//        name: "libfoo",
+//        symbol_file: "libfoo.map.txt",
+//        export_include_dirs: ["include_vndk"],
+//    }
 func LlndkLibraryFactory() android.Module {
 	module := NewLLndkStubLibrary()
 	android.InitAndroidArchModule(module, android.DeviceSupported, android.MultilibBoth)
@@ -203,6 +211,8 @@ func (headers *llndkHeadersDecorator) Name(name string) string {
 	return name + llndkHeadersSuffix
 }
 
+// llndk_headers contains a set of c/c++ llndk headers files which are imported
+// by other soongs cc modules.
 func llndkHeadersFactory() android.Module {
 	module, library := NewLibrary(android.DeviceSupported)
 	library.HeaderOnly()

cc/toolchain_library.go

@@ -48,6 +48,9 @@ func (library *toolchainLibraryDecorator) linkerProps() []interface{} {
 	return append(props, &library.Properties)
 }
 
+// toolchain_library is used internally by the build tool to link the specified
+// static library in src property to the device libraries that are shipped with
+// gcc.
 func ToolchainLibraryFactory() android.Module {
 	module, library := NewLibrary(android.HostAndDeviceSupported)
 	library.BuildOnlyStatic()

cc/vendor_public_library.go

@@ -122,6 +122,15 @@ func (stub *vendorPublicLibraryStubDecorator) link(ctx ModuleContext, flags Flag
 	return stub.libraryDecorator.link(ctx, flags, deps, objs)
 }
 
+// vendor_public_library creates a stub shared library for a vendor public
+// library. This stub library is a build-time only artifact that provides
+// symbols that are exposed from a vendor public library. Example:
+//
+//    vendor_public_library {
+//        name: "libfoo",
+//        symbol_file: "libfoo.map.txt",
+//        export_public_headers: ["libfoo_headers"],
+//    }
 func vendorPublicLibraryFactory() android.Module {
 	module, library := NewLibrary(android.DeviceSupported)
 	library.BuildOnlyShared()