[clang] [FMV] Allow multi versioning without default declaration. (PR #85454)

[Jon Roelofs via cfe-commits]

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@@ -68,13 +68,15 @@ int __attribute__((target_version(""))) unsup1(void) { return 1; }
 void __attribute__((target_version("crc32"))) unsup2(void) {}
 
 void __attribute__((target_version("default+fp16"))) koo(void) {}
+//expected-error at -1 {{function multiversioning doesn't support feature 'default'}}
 void __attribute__((target_version("default+default+default"))) loo(void) {}
+//expected-error at -1 {{function multiversioning doesn't support feature 'default'}}
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jroelofs wrote:

Maybe this should get its own diagnostic. I could see that phrasing being really confusing.

https://github.com/llvm/llvm-project/pull/85454