[clang] [C++20] [Modules] [Itanium ABI] Generate the vtable in the module unit of dynamic classes (PR #75912)

[David Blaikie via cfe-commits]

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@@ -41,9 +43,10 @@ Base::~Base() {}
 // CHECK: @_ZTSW3Mod4Base = constant
 // CHECK: @_ZTIW3Mod4Base = constant
 
-// CHECK-INLINE: @_ZTVW3Mod4Base = linkonce_odr {{.*}}unnamed_addr constant
-// CHECK-INLINE: @_ZTSW3Mod4Base = linkonce_odr {{.*}}constant
-// CHECK-INLINE: @_ZTIW3Mod4Base = linkonce_odr {{.*}}constant
+// With the new Itanium C++ ABI, the linkage of vtables in modules don't need to be linkonce ODR.
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dwblaikie wrote:

right, sorry, was misreading the linkages - I guess `weak` might be applicable? 
> “weak” linkage has the same merging semantics as linkonce linkage, except that unreferenced globals with weak linkage may not be discarded. 
But maybe just normal external linkage is the right thing & we let the linker GC things if the user asks it to. Fair enough.

https://github.com/llvm/llvm-project/pull/75912