Draft: Small change to use of temporary ostringstream to works with clang12
This partially overrides my suggestion !1509 (comment 7240343) as on clang12 you get the error
../GaudiCoreSvc/src/JobOptionsSvc/Parser.cpp:46:74: error: no member named 'str' in 'std::basic_ostream<char>'
const std::string input = ( std::ostringstream{} << stream.rdbuf() ).str();
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
Note that I'm not particularly interested in supporting clang12, but I have some builds of Gaudi master against LCG 103 where we still use clang12.