dump some info from builtins cfg

Author: tgross35

patches/0001-Debug-builtins-output.patch

@@ -0,0 +1,50 @@
+From 337e3a5cbc1e92538f02f50baa971f46d235d20e Mon Sep 17 00:00:00 2001
+From: Trevor Gross <[email protected]>
+Date: Tue, 5 Aug 2025 18:48:23 +0000
+Subject: [PATCH] Debug builtins output
+
+---
+ .../compiler-builtins/configure.rs                  | 13 +++++++++++--
+ 1 file changed, 11 insertions(+), 2 deletions(-)
+
+diff --git a/library/compiler-builtins/compiler-builtins/configure.rs b/library/compiler-builtins/compiler-builtins/configure.rs
+index 9721ddf090c..19a7886f496 100644
+--- a/library/compiler-builtins/compiler-builtins/configure.rs
++++ b/library/compiler-builtins/compiler-builtins/configure.rs
+@@ -47,6 +47,12 @@ pub fn from_env() -> Self {
+             .unwrap_or_else(|e| panic!("failed to run `{cmd:?}`: {e}"));
+         let rustc_cfg = str::from_utf8(&out.stdout).unwrap();
+ 
++        println!("cargo::warning=rustc: {}", env::var("RUSTC").unwrap());
++        for line in rustc_cfg {
++            println!("cargo::warning=cfg: {line}");
++        }
++        // println!("cargo::warning=rustc: {}", env::var("RUSTC").unwrap());
++
+         // If we couldn't query `rustc` (e.g. a custom JSON target was used), make the safe
+         // choice and leave `f16` and `f128` disabled.
+         let rustc_output_ok = out.status.success();
+@@ -55,7 +61,7 @@ pub fn from_env() -> Self {
+         let reliable_f16 =
+             rustc_output_ok && rustc_cfg.lines().any(|l| l == "target_has_reliable_f16");
+ 
+-        Self {
++        let ret = Self {
+             triple,
+             triple_split,
+             os: env::var("CARGO_CFG_TARGET_OS").unwrap(),
+@@ -76,7 +82,10 @@ pub fn from_env() -> Self {
+                 .collect(),
+             reliable_f128,
+             reliable_f16,
+-        }
++        };
++
++        println!("cargo::warning=target: {ret:?}");
++        ret
+     }
+ 
+     #[allow(dead_code)]
+-- 
+2.48.1
+