[clang] [Clang][AArch64] Require SVE or SSVE for scalable types. (PR #91356)

[Paul Walker via cfe-commits]

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@@ -9,6 +9,12 @@
 
 #include <arm_sme.h>
 
+#if defined __ARM_FEATURE_SME
+#define MODE_ATTR __arm_streaming
+#else
+#define MODE_ATTR __arm_streaming_compatible
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paulwalker-arm wrote:

Do you need to use `__arm_streaming_compatible` here?  Now we've agreed this keyword has no effect on the target features in use I think `MODE_ATTR` should remain blank to mirror the expected usage when SME is not in use.

https://github.com/llvm/llvm-project/pull/91356