Add BPF support & C-based BPF tic-tac-toe (#1422)

Add initial support for BPF and a C port of tictactoe

programs/bpf/tictactoe_c/build.sh

@@ -0,0 +1,9 @@
+#!/bin/bash -ex
+
+OUTDIR="${1:-../../../target/release/}"
+THISDIR=$(dirname "$0")
+mkdir -p "$OUTDIR"
+/usr/local/opt/llvm/bin/clang -Werror -target bpf -O2 -emit-llvm -fno-builtin -o "$OUTDIR"/tictactoe_c.bc -c "$THISDIR"/src/tictactoe.c
+/usr/local/opt/llvm/bin/llc -march=bpf -filetype=obj -function-sections -o "$OUTDIR"/tictactoe_c.o "$OUTDIR"/tictactoe_c.bc
+
+# /usr/local/opt/llvm/bin/llvm-objdump -color -source -disassemble "$OUTDIR"/tictactoe_c.o