llvm/bpf: disable llvm builtins for bpf target

As bpf program has no global section for constant values (especially strings),
so use llvm's builtins (like memcpy, memset, etc) will lead to compilation failure
(something like this: A call to built-in function 'memcpy' is not supported.)

Signed-off-by: Tw <tw19881113@gmail.com>

src/codegen/llvm.zig

@@ -2719,6 +2719,9 @@ pub const DeclGen = struct {
         if (comp.bin_file.options.llvm_cpu_features) |s| {
             llvm_fn.addFunctionAttr("target-features", s);
         }
+        if (comp.getTarget().cpu.arch.isBpf()) {
+            llvm_fn.addFunctionAttr("no-builtins", "");
+        }
     }
 
     fn resolveGlobalDecl(dg: *DeclGen, decl_index: Module.Decl.Index) Error!*llvm.Value {