Disambiguate between rustc vs std having debug assertions

Additionally, `NO_DEBUG_ASSERTIONS` is set by CI that threads through to
the `./configure` script, which is somewhat fragile and "spooky action
at a distance". Instead, use env vars controlled by compiletest, whose
debug assertion info comes from bootstrap.

src/tools/compiletest/src/runtest/run_make.rs

@@ -225,6 +225,19 @@ impl TestCx<'_> {
             cmd.env("RUNNER", runner);
         }
 
+        // Guard against externally-set env vars.
+        cmd.env_remove("__RUSTC_DEBUG_ASSERTIONS_ENABLED");
+        if self.config.with_rustc_debug_assertions {
+            // Used for `run_make_support::env::rustc_debug_assertions_enabled`.
+            cmd.env("__RUSTC_DEBUG_ASSERTIONS_ENABLED", "1");
+        }
+
+        cmd.env_remove("__STD_DEBUG_ASSERTIONS_ENABLED");
+        if self.config.with_std_debug_assertions {
+            // Used for `run_make_support::env::std_debug_assertions_enabled`.
+            cmd.env("__STD_DEBUG_ASSERTIONS_ENABLED", "1");
+        }
+
         // We don't want RUSTFLAGS set from the outside to interfere with
         // compiler flags set in the test cases:
         cmd.env_remove("RUSTFLAGS");

src/tools/run-make-support/src/env.rs

@@ -18,11 +18,20 @@ pub fn env_var_os(name: &str) -> OsString {
     }
 }
 
-/// Check if `NO_DEBUG_ASSERTIONS` is set (usually this may be set in CI jobs).
+/// Check if staged `rustc`-under-test was built with debug assertions.
 #[track_caller]
 #[must_use]
-pub fn no_debug_assertions() -> bool {
-    std::env::var_os("NO_DEBUG_ASSERTIONS").is_some()
+pub fn rustc_debug_assertions_enabled() -> bool {
+    // Note: we assume this env var is set when the test recipe is being executed.
+    std::env::var_os("__RUSTC_DEBUG_ASSERTIONS_ENABLED").is_some()
+}
+
+/// Check if staged `std`-under-test was built with debug assertions.
+#[track_caller]
+#[must_use]
+pub fn std_debug_assertions_enabled() -> bool {
+    // Note: we assume this env var is set when the test recipe is being executed.
+    std::env::var_os("__STD_DEBUG_ASSERTIONS_ENABLED").is_some()
 }
 
 /// A wrapper around [`std::env::set_current_dir`] which includes the directory