Fix incorrect NDEBUG handling in LLVM bindings

We currently compile our LLVM bindings using `-DNDEBUG` if
debuginfo for LLVM is disabled. However, `NDEBUG` doesn't have
any relation to debuginfo, it controls whether assertions are
enabled.

Rename the environment variable to `LLVM_ASSERTIONS` and drive
it using the `llvm_assertions` option. Also drop the explicit
`debug(false)` call, as cc already sets this up using the
cargo `DEBUG` environment variable.

Author: nikic

compiler/rustc_llvm/build.rs

@@ -197,9 +197,8 @@ fn main() {
         cfg.define("LLVM_RUSTLLVM", None);
     }
 
-    if tracked_env_var_os("LLVM_NDEBUG").is_some() {
+    if tracked_env_var_os("LLVM_ASSERTIONS").is_none() {
         cfg.define("NDEBUG", None);
-        cfg.debug(false);
     }
 
     rerun_if_changed_anything_in_dir(Path::new("llvm-wrapper"));

src/bootstrap/src/core/build_steps/compile.rs

@@ -1213,8 +1213,8 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
     if builder.config.llvm_use_libcxx {
         cargo.env("LLVM_USE_LIBCXX", "1");
     }
-    if builder.config.llvm_optimize && !builder.config.llvm_release_debuginfo {
-        cargo.env("LLVM_NDEBUG", "1");
+    if builder.config.llvm_assertions {
+        cargo.env("LLVM_ASSERTIONS", "1");
     }
 }