[PATCH, v2] ARM: fix inline atomic handling

[Tim Northover]

Hi Phoebe,

+    // Cortex M does not support 8 byte atomics, while general Thumb2 does.
+    StringRef Profile = getCPUProfile(Name);
+    if (Profile == "M" && MaxAtomicInlineWidth) {
+      MaxAtomicPromoteWidth = 32;
+      MaxAtomicInlineWidth = 32;
+    }

This seems like a fairly key point of the patch (it's what inspired
you to start working on this area isn't it?), but it's not tested; it
would be good to see some checks that the 64-bit case is handled as
expected.

Cheers.

Tim.