Minor enhancements to the Android build system

Minor enhancements to the Android build system

* build-aux/ndk-build-helper-1.mk:

* build-aux/ndk-build-helper-2.mk:

* cross/ndk-build/ndk-build-shared-library.mk:

* cross/ndk-build/ndk-build-static-library.mk:

* cross/ndk-build/ndk-resolve.mk
(NDK_SO_EXTRA_FLAGS_$(LOCAL_MODULE)):
(NDK_LOCAL_SO_NAMES_$(LOCAL_MODULE)):
(NDK_LOCAL_A_NAMES_$(LOCAL_MODULE)): Reinforce tests for string
prefixes.

* m4/ndk-build.m4 (ndk_INIT): Guarantee that a module's
dependencies are recorded.

* configure.ac (XCONFIGURE): Prepare for building librsvg.

(cherry picked from commit a48f062e36be3ce5890a8a789272f31f074fea40)