Add libtiff support to Android port

Add libtiff support to Android port

* INSTALL.android: Document how to build with libtiff.

* build-aux/ndk-build-helper-1.mk (NDK_SO_NAME):
* build-aux/ndk-build-helper-2.mk (NDK_A_NAME):
* build-aux/ndk-build-helper-4.mk: Decrease number of duplicate
dependencies found.
* configure.ac (ANDROID_SDK_18_OR_EARLIER, XCONFIGURE, PNG_CFLAGS)
(HAVE_TIFF): Allow using libtiff on Android.
* cross/ndk-build/ndk-clear-vars.mk: Undefine additional
variables.
* cross/ndk-build/ndk-resolve.mk: Split CFLAGS resolution from
a-name resolution, and do not recursively add archive or shared
object names for dependencies of shared libraries.

* src/Makefile.in (TIFF_CFLAGS): New variable.
(EMACS_CFLAGS): Use it.