Remove deprecated whitespace in literal operator declaration

[r0qs]

This should fix the issues we are currently having in CI: https://app.circleci.com/pipelines/github/ethereum/solidity/39752/workflows/b911322a-7204-47c5-a2c7-0e24ba30afe1/jobs/1841317

#11 11.62 /solidity/liblangutil/Exceptions.h:166:30: error: identifier '_error' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
#11 11.62   166 | constexpr ErrorId operator"" _error(unsigned long long _error) { return ErrorId{ _error }; }
#11 11.62       |                   ~~~~~~~~~~~^~~~~~
#11 11.62       |                   operator""_error

See https://reviews.llvm.org/D153156 and llvm/llvm-project#111027

And about the deprecation: https://cplusplus.github.io/CWG/issues/2521.html

Not sure if we need to maintain compatibility with old GCC, but if so, we may need to add some preprocessor directives like in:
apache/arrow-nanoarrow#661 (comment)