Update Android port

Update Android port

ImageMagick now builds but does not link yet some of the time.

* INSTALL.android: Document ImageMagick and caveats.
* build-aux/ndk-build-helper-1.mk (NDK_SO_NAMES):
* build-aux/ndk-build-helper-2.mk (NDK_A_NAMES):
* build-aux/ndk-build-helper.mk (TARGET_ARCH_ABI): Define architecture
and don't respect explicitly specified library names.
* configure.ac: Enable ImageMagick and lcms2 on Android.
* cross/ndk-build/ndk-build-shared-library.mk (objname)::($(call
objname,$(LOCAL_MODULE),$(basename
$(1))))::(ALL_OBJECT_FILES$(LOCAL_MODULE)):
* cross/ndk-build/ndk-build-static-library.mk (objname)::($(call
objname,$(LOCAL_MODULE),$(basename $(1)))):
(NDK_CFLAGS, ALL_SOURCE_FILES): Handle sources files which start with
$(LOCAL_PATH).
* cross/ndk-build/ndk-clear-vars.mk: Don't undefine; clear variables
instead.
* m4/ndk-build.m4 (ndk_SEARCH_MODULE): Redirect make stderr to
config.log.xf64