Improve support for building Android C++ dependencies

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.