Ceph

with gcc-12 and -std=c++2b, the crimson build fails:

-std=c++2b -MD -MT src/crimson/CMakeFiles/crimson-common.dir/__/common/LogEntry.cc.o -MF src/crimson/CMakeFiles/crimson-common.dir/__/common/LogEntry.cc.o.d -o src/crimson/CMakeFiles/crimson-common.dir/__/common/LogEntry.cc.o -c /home/jenkins-build/build/workspace/ceph-pull-requests/src/common/LogEntry.cc
/home/jenkins-build/build/workspace/ceph-pull-requests/src/common/LogEntry.cc:186:14: error: conversion function from 'int' to 'std::string' (aka 'basic_string<char>') invokes a deleted function
      return 0;
             ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/basic_string.h:742:7: note: 'basic_string' has been explicitly marked deleted here
      basic_string(nullptr_t) = delete;
      ^
1 error generated.

i can't tell where -std=c++2b is coming from, and that seems wrong, but the fix is easy enough (don't return 0; there)