Revised yield hints

Turns out v7 targets always have v6t2 set, so that line was redundant. Also add a link to the Arm Armv7 A.R.M.

Author: thejpster

library/core/src/hint.rs

@@ -298,11 +298,12 @@ pub fn spin_loop() {
                 all(target_feature = "v6k", not(target_feature = "thumb-mode")),
                 target_feature = "v6t2",
                 all(target_feature = "v6", target_feature = "mclass"),
-                target_feature = "v7",
             )
         ) => {
-            // SAFETY: the `cfg` attr ensures that we only execute this on arm targets
-            // with support for the v6 feature.
+            // SAFETY: the `cfg` attr ensures that we only execute this on arm
+            // targets with support for the this feature. On ARMv6 in Thumb
+            // mode, T2 is required (see Arm DDI0406C Section A8.8.427),
+            // otherwise ARMv6-M or ARMv6K is enough
             unsafe { crate::arch::arm::__yield() }
         }
         target_arch = "loongarch32" => crate::arch::loongarch32::ibar::<0>(),

library/stdarch/crates/core_arch/src/arm_shared/hints.rs

@@ -83,12 +83,11 @@ pub unsafe fn __sevl() {
 /// improve overall system performance.
 // Section 10.1 of ACLE says that the supported arches are: 8, 6K, 6-M
 // LLVM says "instruction requires: armv6k"
-// On ARMv6 in Thumb mode, T2 is required.
+// On ARMv6 in Thumb mode, T2 is required (see Arm DDI0406C Section A8.8.427)
 #[cfg(any(
     all(target_feature = "v6k", not(target_feature = "thumb-mode")),
     target_feature = "v6t2",
     all(target_feature = "v6", target_feature = "mclass"),
-    target_feature = "v7",
     target_arch = "aarch64",
     target_arch = "arm64ec",
     doc