Improve support for building Android C++ dependencies

* configure.ac: Call ndk_LATE after gl_EARLY.
* cross/ndk-build/Makefile.in (NDK_BUILD_CXX): New variable.
* cross/ndk-build/ndk-build-shared-library.mk:
* cross/ndk-build/ndk-build-static-library.mk: Use it.
* java/INSTALL: Describe how to build C++ dependencies.
* m4/ndk-build.m4 (ndk_LATE): New macro.
(ndk_INIT): Try to find a suitable C++ compiler.
(ndk_CHECK_MODULES): Make sure the C++ compiler works before
allowing C++ dependencies.

java/INSTALL

@@ -111,6 +111,24 @@ Emacs package cannot be compressed in builds for Android 2.2.  As a
 result, the Emacs package will be approximately 100 megabytes larger
 than a compressed package for a newer version of Android.
 
+
+BUILDING C++ DEPENDENCIES
+
+With a new version of the NDK, dependencies containing C++ code should
+build without any futher configuration.  However, older versions
+require that you use the ``make_standalone_toolchain.py'' script in
+the NDK distribution to create a ``standalone toolchain'', and use
+that instead, in order for C++ headers to be found.
+
+See https://developer.android.com/ndk/guides/standalone_toolchain for
+more details; when a ``standalone toolchain'' is specified, the
+configure script will try to determine the location of the C++
+compiler based on the C compiler specified.  If that automatic
+detection does not work, you can specify a C++ compiler yourself, like
+so:
+
+  ./configure --with-ndk-cxx=/path/to/toolchain/bin/i686-linux-android-g++
+
 
 DEBUG AND RELEASE BUILDS