Add more detailed comment

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 865e18b..61233f8 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -3480,7 +3480,12 @@
     # armc[56] don't support SHA-512 intrinsics
     scripts/config.py unset MBEDTLS_SHA512_USE_A64_CRYPTO_IF_PRESENT
 
-    # stop armclang warning about feature detection for A64_CRYPTO
+    # Stop armclang warning about feature detection for A64_CRYPTO.
+    # With this enabled, the library does build correctly under armclang,
+    # but in baremetal builds (as tested here), feature detection is
+    # unavailable, and the user is notified via a #warning. So enabling
+    # this feature would prevent us from building with -Werror on
+    # armclang. Tracked in #7198.
     scripts/config.py unset MBEDTLS_SHA256_USE_A64_CRYPTO_IF_PRESENT
 
     scripts/config.py set MBEDTLS_HAVE_ASM