Compiler Error when using boost fusion, catch2 and a print function

**Describe the bug**
Compiler error when defining a boost fusion struct a free operator<< function before including '#include ' and calling REQUIRE(std::vector{}==std::vector{}).

**Expected behavior**
Should compile.

**Reproduction steps**
[Code which reproduces the error](https://godbolt.org/z/sY7hYzjT3)

1. define a boost fusion struct
2. define 'inline std::ostream &operator<< (std::ostream &os, shared_class::Nested const &nested);'
3. include 'catch2/catch_test_macros.hpp'
4. Create a TEST_CASE and call 'REQUIRE (std::vector{} == std::vector{}); '