HACK: rust: x86: Set data-layout based on rustc's LLVM version

LLVM changed the data layout in x86 between 17 and 18 but Rust 1.77.0
and later checks for matching data layouts.

Parse the used LLVM version from `rustc -v --version` and generate a
matching target.json based on that.

We might need to keep this even with rust 1.78 depending ron the rust
package in Fedora 39.

Link: https://lore.kernel.org/lkml/20240401212303.537355-4-ojeda@kernel.org/
Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

init/Kconfig

@@ -1927,6 +1927,11 @@ config RUSTC_VERSION_TEXT
 	depends on RUST
 	default $(shell,command -v $(RUSTC) >/dev/null 2>&1 && $(RUSTC) --version || echo n)
 
+config RUSTC_LLVM_VERSION_TEXT
+	string
+	depends on RUST
+        default $(shell,command -v $(RUSTC) >/dev/null 2>&1 && $(RUSTC) -v --version | grep '^LLVM version' | sed -e 's/^.*: *//' || echo n)
+
 config BINDGEN_VERSION_TEXT
 	string
 	depends on RUST

scripts/generate_rust_target.rs

@@ -152,10 +152,23 @@ fn main() {
         panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
     } else if cfg.has("X86_64") {
         ts.push("arch", "x86_64");
+        let mut llvm_version: u32 = 18;
+        if cfg.has("RUSTC_LLVM_VERSION_TEXT") {
+            let llvm_str = cfg.0.get("CONFIG_RUSTC_LLVM_VERSION_TEXT").unwrap().split_once(".").unwrap().0;
+            llvm_version = llvm_str.parse().unwrap();
+        }
+        // intentially broken indent
+        if llvm_version >= 18 {
+        ts.push(
+            "data-layout",
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
+        );
+        } else {
         ts.push(
             "data-layout",
             "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128",
         );
+        }
         let mut features = "-3dnow,-3dnowa,-mmx,+soft-float".to_string();
         if cfg.has("RETPOLINE") {
             features += ",+retpoline-external-thunk";