Fix ImageMagick build on Android

Fix ImageMagick build on Android

* INSTALL.android (-linux_arm_sources):
* build-aux/ndk-build-helper-1.mk:
(NDK_$(LOCAL_MODULE)_STATIC_LIBRARIES)::(NDK_CXX_FLAG_$(LOCAL_MODULE)):
* build-aux/ndk-build-helper-2.mk:
(NDK_$(LOCAL_MODULE)_STATIC_LIBRARIES)::(NDK_CXX_FLAG_$(LOCAL_MODULE)):
* 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
$(1))))::(ALL_OBJECT_FILES$(LOCAL_MODULE)):
(ALL_SOURCE_FILES): Update ImageMagick build instructions and
C++ module detection.