[clang] [clang][SME] Rework streaming mode always_inline errors/warnings (PR #174608)

[Benjamin Maxwell via cfe-commits]

================
@@ -1327,12 +1327,15 @@ def PerfConstraintImpliesNoexcept : DiagGroup<"perf-constraint-implies-noexcept"
 // Uniqueness Analysis warnings
 def Consumed       : DiagGroup<"consumed">;
 
+// A warning group related to AArch64 SME function attribues.
+def AArch64SMEAttributes : DiagGroup<"aarch64-sme-attributes">;
+
 // Note that putting warnings in -Wall will not disable them by default. If a
 // warning should be active _only_ when -Wall is passed in, mark it as
 // DefaultIgnore in addition to putting it here.
 def All : DiagGroup<"all", [Most, Parentheses, Switch, SwitchBool,
                             MisleadingIndentation, PackedNonPod,
-                            VLACxxExtension]>;
+                            VLACxxExtension, AArch64SMEAttributes]>;
----------------
MacDue wrote:

Not sure if this should be included in `-Wall`. If not, the warning would require `-Waarch64-sme-attributes` (which may be hard to discover). 

https://github.com/llvm/llvm-project/pull/174608