Fix out-of-tree Android builds

Fix out-of-tree Android builds

* configure.ac (JAVA_PUSH_LINT): Push to WARN_JAVAFLAGS instead
of JAVAFLAGS.
(cross/lib): Always AS_MKDIR_P.
* cross/Makefile.in (srcdir): New variable.
(LIB_SRCDIR): Take realpath relative to srcdir, not
.:(src/verbose.mk): Depend on verbose.mk.android in srcdir.
(lib/Makefile): Edit srcdir and VPATH to LIB_SRCDIR.
(src/Makefile): Edit -I$$(top_srcdir) to -I../$(srcdir)/lib,
instead of ommitting it.
(clean): Allow ndk-build clean to fail.

* java/Makefile.in (builddir): New variable.
(WARN_JAVAFLAGS): Likewise.
(JAVAFLAGS): Define in terms of WARN_JAVAFLAGS.
(SIGN_EMACS, SIGN_EMACS_V2): Use emacs.keystore relative to
srcdir.  Allow inclusion of ndk-build.mk to fail.
(install_temp, emacs.apk-in)
(../config.status): Depend relative to top_srcdir.
(AndroidManifest.xml, $(APK_NAME)): Likewise.
(RESOURCE_FILE, CLASS_FILES, classes.dex): Output class files
to $(srcdir); these are arch independents, so this is okay.