Auto merge of #131077 - lqd:debug-assertions-alt, r=<try>

Enable debug assertions on alt builds

Alt builds already have llvm assertions enabled, and this PR adds rustc's debug assertions.

We've discussed that this would be useful a few times in the past, most recently in [this zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp/topic/cargo.20bisect-rustc'ing.20a.20debug.20assertions-only.20ICE), for example to bisect the source PR of an unexpected tripped debug assert, which is not that rare of an occurrence.

[In another thread](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Alt.20builds.20with.20debug.20assertions) we discussed how it would help with Matthias' fuzzing workflow, and some of Ben's work.

I don't _believe_ this needs an MCP, but am not sure.

To my knowledge there are 2 alt builds (x64 linux, x64 msvc) and this enables it for both, though we could limit to x64 linux if we wanted to.

try-job: dist-x86_64-linux-alt
try-job: dist-x86_64-msvc-alt

Author: bors

src/ci/run.sh

@@ -131,6 +131,11 @@ if [ "$DEPLOY$DEPLOY_ALT" = "1" ]; then
 
   CODEGEN_BACKENDS="${CODEGEN_BACKENDS:-llvm}"
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.codegen-backends=$CODEGEN_BACKENDS"
+
+  # Unless explicitly disabled, we want rustc debug assertions on the -alt builds
+  if [ "$DEPLOY_ALT" != "" ] && [ "$NO_DEBUG_ASSERTIONS" = "" ]; then
+    RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-debug-assertions"
+  fi
 else
   # We almost always want debug assertions enabled, but sometimes this takes too
   # long for too little benefit, so we just turn them off.