Fix missing library template parameter in IR codegen on EOF

[cameel]

Fixes a small bug that went unnoticed in #15512 because we don't run most tests on EOF yet: the IR codegen template is missing a parameter.

Running tests for immutables without the fix results in:

semanticTests/immutable/stub.sol: Unhandled exception during test: /solidity/libsolutil/Whiskers.cpp(213): Throw in function solidity::util::Whiskers::replace(const std::string&, const StringMap&, const std::map<std::__cxx11::basic_string<char>, bool>&, const std::map<std::__cxx11::basic_string<char>, std::vector<std::map<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char> > > >&)::<lambda(std::__cxx11::match_results<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> > >)>
Dynamic exception type: boost::wrapexcept<solidity::util::WhiskersError>
std::exception::what: WhiskersError
[solidity::util::tag_comment*] = Condition parameter library not set.

I'm also including a commit that makes the test mentioned in #15550 (review) actually run on EOF too.

[cameel]

Oh, looks like that wasn't the only bug here:

/solidity/test/soltest.cpp(120): error: in "semanticTests/immutable/stub": Exception during extracted test: /solidity/libsolidity/codegen/ir/IRGenerationContext.cpp(103): Throw in function size_t solidity::frontend::IRGenerationContext::immutableMemoryOffset(const solidity::frontend::VariableDeclaration&) const
Dynamic exception type: boost::wrapexcept<solidity::langutil::InternalCompilerError>
std::exception::what: Unknown immutable variable: x
[solidity::util::tag_comment*] = Unknown immutable variable: x