Generate Android shared library list automatically

Generate Android shared library list automatically

* .gitignore: Ignore new generated files.

* cross/Makefile.in (src/Makefile): Remove leftover
specification of the source Gnulib directory.

* cross/ndk-build/ndk-build.mk.in (NDK_BUILD_READELF): New
variable.

* java/Makefile.in (CONFIG_FILE, ALL_DEPENDENCIES, READELF)
(cf-stamp-1, cf-stamp): New variables and rules; compute the set
of library files in the order of loading and generate a file
with this information.
(ALL_CLASS_FILES): New variable; if builddir is not srcdir,
$($(CONFIG_FILE), $(CLASS_FILES)): Depend on EmacsConfig.java.
add generated files in the build directory.
(classes.dex): Adjust to match.

* java/org/gnu/emacs/EmacsNative.java (EmacsNative)
<static initializer>: Load shared libraries from
EMACS_SHARED_LIBRARIES rather than a hard-coded list.

* m4/ndk-build.m4 (ndk_INIT): Search for readelf...
(ndk_CHECK_MODULES): ...and substitute its path as
NDK_BUILD_READELF.