[small tip][bash] Autocomplete ignore the `mlir-c` directory

MLIR’s directory structure has include/mlir but also include/mlir-c which I’ve always found causes a little glitch for me when autocompleting (same for llvm-c in LLVM). Turns out there’s a small bash hack that can solve this minor inconvenience for those of us that spend a lot of time on the command line.

# Ignore llvm-c and mlir-c directories.
# See here for more info on the incantation:
# https://stackoverflow.com/a/34272881
# https://superuser.com/q/253068
export FIGNORE=$FIGNORE:lvm-c:lir-c