Disable jit and inline-asm when building as part of rustc

Both features are not yet ready. Inline-asm is only supported on Linux
and requires explicitly specifying registers instead of register
classes. The jit has usability issues and may require the cg_clif
executable in the future.

Author: bjorn3

Cargo.toml

@@ -37,7 +37,8 @@ smallvec = "1.6.1"
 #gimli = { path = "../" }
 
 [features]
-default = ["jit", "inline_asm"]
+# Enable features not ready to be enabled when compiling as part of rustc
+unstable-features = ["jit", "inline_asm"]
 jit = ["cranelift-jit", "libloading"]
 inline_asm = []
 

build_system/build_backend.rs

@@ -4,7 +4,7 @@ use std::process::Command;
 
 pub(crate) fn build_backend(channel: &str, host_triple: &str) -> PathBuf {
     let mut cmd = Command::new("cargo");
-    cmd.arg("build").arg("--target").arg(host_triple);
+    cmd.arg("build").arg("--target").arg(host_triple).arg("--features").arg("unstable-features");
 
     match channel {
         "debug" => {}