Fix build?

Author: Byron

crates/core_arch/src/arm/mod.rs

@@ -97,6 +97,8 @@ pub unsafe fn udf() -> ! {
 // and ARMv7-R edition (ARM DDI 0406C.c) sections D12.4.1 "ARM instruction set support" and D12.4.2
 // "Thumb instruction set support"
 #[cfg(any(target_feature = "v7", doc))]
+#[cfg(any(target_arch = "arm", doc))]
+#[doc(cfg(target_arch = "arm"))]
 #[inline(always)]
 #[rustc_legacy_const_generics(0)]
 pub unsafe fn __dbg<const IMM4: i32>() {