Add support for packaging static libs in the NDK.

Adding `static_ndk_lib: true` to a module installs the static library
to the NDK sysroot.

Test: Set property for libc.a, make ndk
Test: Set property for libc.a, scripts/build-ndk-prebuilts.sh
Bug: https://github.com/android-ndk/ndk/issues/272
Change-Id: Ib368a25705f2adb7129dac207c1b727d4ccc1eb2

cc/ndk_sysroot.go

@@ -108,6 +108,12 @@ func (n *ndkSingleton) GenerateBuildActions(ctx blueprint.SingletonContext) {
 			if installer, ok := m.installer.(*stubDecorator); ok {
 				installPaths = append(installPaths, installer.installPath)
 			}
+
+			if library, ok := m.linker.(*libraryDecorator); ok {
+				if library.MutatedProperties.NdkSysrootPath != "" {
+					installPaths = append(installPaths, library.MutatedProperties.NdkSysrootPath)
+				}
+			}
 		}
 	})