Unity have implemented fully generic shared function generation, when generic params could be both reference types or struct types to generate less code, but when calli opcode is encountered with an unmanaged call it will generate exception. Though it's ok because we don't need fully generic sharing, we always know argument types upfront. This exception throw will fully replace the call.
And by "fully" I mean FULLY. Yes, with returning value too. Then it referencing intptr_t L_11 which should be a return value, and since it's now non-existent, well, the variable became non-existent too leading to compile errors. This is only the case when TReturn is a reference type, of there's no TReturn at all (returning a void* for instance)