Fix compilation error seen with gcc 12.0.1 on Fedora 36:
In file included from ../libs/ardour/ardour/variant.h:30,
from ../libs/ardour/ardour/parameter_descriptor.h:25,
from ../libs/ardour/ardour/automation_control.h:39,
from ../libs/ardour/ardour/amp.h:30,
from ../libs/ardour/session.cc:61:
../libs/pbd/pbd/compose.h: In instantiation of ‘StringPrivate::Composition& StringPrivate::Composition::arg(const T&) [with T = ARDOUR::PresentationInfo]’:
../libs/pbd/pbd/compose.h:277:31: required from ‘std::string string_compose(const std::string&, const T1&, const T2&, const T3&, const T4&) [with T1 = std::__cxx11::basic_string<char>; T2 = unsigned int; T3 = std::__cxx11::basic_string<char>; T4 = ARDOUR::PresentationInfo; std::string = std::__cxx11::basic_string<char>]’
../libs/ardour/session.cc:3268:4: required from here
../libs/pbd/pbd/compose.h:122:20: error: no match for ‘operator<<’ (operand types are ‘std::ostringstream’ {aka ‘std::__cxx11::basic_ostringstream<char>’} and ‘const ARDOUR::PresentationInfo’)
122 | os << obj;
| ~~~^~~~~~
This might also fix a similar problem with clang, and
https://github.com/Ardour/ardour/commit/5bbfac23808 can be backed out.
217519b1b4