Auto merge of #79608 - alessandrod:bpf, r=nagisa

BPF target support

This adds `bpfel-unknown-none` and `bpfeb-unknown-none`, two new no_std targets that generate little and big endian BPF. The approach taken is very similar to the cuda target, where `TargetOptions::obj_is_bitcode` is enabled and code generation is done by the linker.

I added the targets to `dist-various-2`. There are [some tests](https://github.com/alessandrod/bpf-linker/tree/main/tests/assembly) in bpf-linker and I'm planning to add more. Those are currently not ran as part of rust CI.

compiler/rustc_llvm/build.rs

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

compiler/rustc_llvm/src/lib.rs

@@ -167,4 +167,12 @@ pub fn initialize_available_targets() {
         LLVMInitializeWebAssemblyAsmPrinter,
         LLVMInitializeWebAssemblyAsmParser
     );
+    init_target!(
+        llvm_component = "bpf",
+        LLVMInitializeBPFTargetInfo,
+        LLVMInitializeBPFTarget,
+        LLVMInitializeBPFTargetMC,
+        LLVMInitializeBPFAsmPrinter,
+        LLVMInitializeBPFAsmParser
+    );
 }