Specifically, consider:

    capnp::BuilderFor<capnp::DynamicStruct> capnp::Orphan<capnp::AnyPointer>::getAs<capnp::DynamicStruct>(capnp::StructSchema)

Note that `BuilderFor` is a "template using" directive which expands into something more complicated.

GCC mangles the symbol as:

    _ZN5capnp6OrphanINS_10AnyPointerEE5getAsINS_13DynamicStructEEENS_11BuilderFor_IT_Xcl4kindIS6_EEEE4TypeENS_12StructSchemaE

Which `c++filt` decodes as:

    capnp::BuilderFor_<capnp::DynamicStruct, (kind<capnp::DynamicStruct>)()>::Type capnp::Orphan<capnp::AnyPointer>::getAs<capnp::DynamicStruct>(capnp::StructSchema)

Note that `BuilderFor_<...>::Type` here ends up being a typedef for `DynamicStruct::Builder`. It seems weird to me that the symbol name would not substitute this typedef.

Clang, meanwhile, mangles the symbol as:

    _ZN5capnp6OrphanINS_10AnyPointerEE5getAsINS_13DynamicStructEEENS_11BuilderFor_IT_Xclgssr5capnpE4kindIS6_EEEE4TypeENS_12StructSchemaE

Which `c++filt` does not seem to be able to demangle at all. But, it looks like `capnp::kind` is in there, suggesting that, again, the typedef wasn't substituted.

I don't know who is right, but if we inline the whole thing, the problem goes away.