Don't load compiler_rt if renderscript is disabled

Bug: 206676167
Test: Verified on aosp_cf_riscv64_slim target, which doesn't support RS,
that this library loads and fails by default, but skips load when the
config.disable_renderscript flag is enabled.

Change-Id: If3f516f5e38c39b35b26d102ebdc9a4816be60a3