rust: export build_error symbol if RUST_BUILD_ASSERT_DENY is not set

This ensures that under `RUST_BUILD_ASSERT_WARN` or
`RUST_BUILD_ASSERT_ALLOW`, modpost will not reject modules containing
call to `rust_build_error`.

Signed-off-by: Gary Guo <[email protected]>

Author: nbdd0121

rust/build_error.rs

@@ -17,13 +17,13 @@
 /// Panics if executed in const context, or triggers a build error if not.
 #[inline(never)]
 #[cold]
-#[no_mangle]
+#[export_name = "rust_build_error"]
 #[track_caller]
 pub const fn build_error(msg: &'static str) -> ! {
     panic!("{}", msg);
 }
 
 #[cfg(CONFIG_RUST_BUILD_ASSERT_WARN)]
-#[link_section = ".gnu.warning.build_error"]
+#[link_section = ".gnu.warning.rust_build_error"]
 #[used]
 static BUILD_ERROR_WARNING: [u8; 45] = *b"call to build_error present after compilation";