Add Android cdylib build support
Gate Java-shell Android sources behind CODECS_STATIC so the cdylib
build uses small headless stubs instead of JNI/Java files. Add
cdylib-specific hosted pieces (system-android, pcm-aaudio, lc-android,
lcd/button no-ops, adc-target.h) and minor rb_zig_compat fixes.
Skip the cRSID codec on NDK clang builds. tools/configure now exports
CODECS_STATIC and -DZIG_APP for Android ndk builds; sigevent_t is
provided via a compile-time -D instead of a typedef in config.h.