Add CFI ignore file for ATfE.

[vrukesh]

Add CFI ignore file for ATfE. This fixes an issue observed with 1ce2517

There are at least 3 ways by which cfi-ignore file can be invoked:

1. With the binary installer, by executing the program. For example: clang --target=aarch64-none-elf -march=armv8-a -c test.c -flto -fsanitize=cfi -fvisibility=hidden
2. With the binary installer, by executing the "cpp-baremetal-semihosting-cfi" example code in "samples" directory, without "-fno-sanitize-ignorelist" in MakeFile
3. By compiling the source code and using the compiled binary to execute the program. For example: ./build/llvm/bin/clang --target=aarch64-none-elf -march=armv8-a -c test.c -flto -fsanitize=cfi -fvisibility=hidden

Previous patch version did not work for scenario 3, and this patch version fixes it.

[pratlucas]

Please update the PR description to cover what was the issue observed with the previous commit, so it's clear for future readers.