Adds the -fsanitize-blacklist option for CFI, using the built in
blacklist at external/compiler-rt/lib/cfi/cfi_blacklist.txt.
Also refactors the CFI cflags and ldflags into cc/makevars.go to
ensure they're consistent across Soong and make projects.
Bug: 30227045
Test: ENABLE_CFI=true m -j40 builds and boots.
Test: The blacklist prevents runtime errors that otherwise occur.
Change-Id: I91c5420478e7290061d89338a86abdef69c67fe2