Add minor fixes for cross-platform support

[Gnimuc]

• Add __CYGWIN__ to allow it to be built in a cygwin environment
• Only enable default visibility for gcc
• Fix CPPINTEROP_API typos

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.22%. Comparing base (86a9f46) to head (452cd94).

Additional details and impacted files

[](https://app.codecov.io/gh/compiler-research/CppInterOp/pull/301?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=compiler-research) ```diff @@ Coverage Diff @@ ## main #301 +/- ## ======================================= Coverage 72.22% 72.22% ======================================= Files 8 8 Lines 2963 2963 ======================================= Hits 2140 2140 Misses 823 823 ``` | [Files](https://app.codecov.io/gh/compiler-research/CppInterOp/pull/301?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=compiler-research) | Coverage Δ | | |---|---|---| | [include/clang/Interpreter/CppInterOp.h](https://app.codecov.io/gh/compiler-research/CppInterOp/pull/301?src=pr&el=tree&filepath=include%2Fclang%2FInterpreter%2FCppInterOp.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=compiler-research#diff-aW5jbHVkZS9jbGFuZy9JbnRlcnByZXRlci9DcHBJbnRlck9wLmg=) | `96.00% <ø> (ø)` | | | [Files](https://app.codecov.io/gh/compiler-research/CppInterOp/pull/301?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=compiler-research) | Coverage Δ | | |---|---|---| | [include/clang/Interpreter/CppInterOp.h](https://app.codecov.io/gh/compiler-research/CppInterOp/pull/301?src=pr&el=tree&filepath=include%2Fclang%2FInterpreter%2FCppInterOp.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=compiler-research#diff-aW5jbHVkZS9jbGFuZy9JbnRlcnByZXRlci9DcHBJbnRlck9wLmg=) | `96.00% <ø> (ø)` | |

[maximusron]

@Gnimuc I've applied clang-format that was causing one of the checks to fail and rebased, should be good to merge once the checks are done. Thanks for the PR!

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"