Disable LTO and CFI for riscv64

Building with LTO and CFI enabled for riscv64 causes link failures:
ld.lld: error: lto.tmp: cannot link object files with different floating-point ABI
ld.lld: error: undefined symbol: guard variable for android::hardware::BufferedTextOutput::getBuffer() const::ts

Disable them for now.

Test: lunch aosp_riscv64-userdebug && m ALLOW_MISSING_DEPENDENCIES=true ndk_sysroot
Change-Id: I3489952abebeeb3f4de664fd3e436232aac298d7