Add BPF target

This change adds the bpfel-unknown-none and bpfeb-unknown-none targets
which can be used to generate little endian and big endian BPF

compiler/rustc_llvm/build.rs

@@ -86,6 +86,7 @@ fn main() {
         "nvptx",
         "hexagon",
         "riscv",
+        "bpf",
     ];
 
     let required_components = &[