Fix compile warning on Apple M1

[BrettDong]

In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/src/detail/backend/BackendWorker.cpp:1:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/backend/BackendWorker.h:13:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/LoggerCollection.h:9:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Logger.h:18:
/Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/misc/Rdtsc.h:34:10: warning: implicit conversion changes signedness: 'int64_t' (aka 'long long') to 'uint64_t' (aka 'unsigned long long') [-Wsign-conversion]
  return virtual_timer_value;
  ~~~~~~ ^~~~~~~~~~~~~~~~~~~
1 warning generated.
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/src/detail/misc/RdtscClock.cpp:3:
/Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/misc/Rdtsc.h:34:10: warning: implicit conversion changes signedness: 'int64_t' (aka 'long long') to 'uint64_t' (aka 'unsigned long long') [-Wsign-conversion]
  return virtual_timer_value;
  ~~~~~~ ^~~~~~~~~~~~~~~~~~~
1 warning generated.
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/src/detail/LoggerCollection.cpp:1:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/LoggerCollection.h:9:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Logger.h:18:
/Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/misc/Rdtsc.h:34:10: warning: implicit conversion changes signedness: 'int64_t' (aka 'long long') to 'uint64_t' (aka 'unsigned long long') [-Wsign-conversion]
  return virtual_timer_value;
  ~~~~~~ ^~~~~~~~~~~~~~~~~~~
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/src/detail/SignalHandler.cpp:8:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Quill.h:12:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/LogMacros.h:10:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Logger.h:18:
/Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/misc/Rdtsc.h:34:10: warning: implicit conversion changes signedness: 'int64_t' (aka 'long long') to 'uint64_t' (aka 'unsigned long long') [-Wsign-conversion]
  return virtual_timer_value;
  ~~~~~~ ^~~~~~~~~~~~~~~~~~~
1 warning generated.
1 warning generated.
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/src/Quill.cpp:1:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Quill.h:12:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/LogMacros.h:10:
In file included from /Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/Logger.h:18:
/Users/jenkins/w/prod/BuildSingleReference@2/.conan/data/quill/2.9.0/_/_/build/182ec311e04295bce36a12820ce7004d2a380991/src/quill/include/quill/detail/misc/Rdtsc.h:34:10: warning: implicit conversion changes signedness: 'int64_t' (aka 'long long') to 'uint64_t' (aka 'unsigned long long') [-Wsign-conversion]
  return virtual_timer_value;
  ~~~~~~ ^~~~~~~~~~~~~~~~~~~
1 warning generated.

https://c3i.jfrog.io/c3i/misc/logs/pr/17550/1-macos-m1-clang/quill/2.9.0//182ec311e04295bce36a12820ce7004d2a380991-build.txt

[odygrd]

thanks for the PR 👍