[OE-core] [PATCH 02/15] libdnf: upgrade 0.28.1 -> 0.38.1

[Ross Burton]

FAILED: libdnf/CMakeFiles/libdnf.dir/dnf-context.cpp.o
/home/pokybuild/yocto-worker/buildtools/build/build/tmp/work/x86_64-linux/libdnf-native/0.38.1-r0/git/libdnf/dnf-context.cpp:2618:8: 
error: ‘atomic_flag’ in namespace ‘std’ does not name a type
  static std::atomic_flag cfgMainLoaded = ATOMIC_FLAG_INIT;
         ^
/home/pokybuild/yocto-worker/buildtools/build/build/tmp/work/x86_64-linux/libdnf-native/0.38.1-r0/git/libdnf/dnf-context.cpp: 
In function ‘libdnf::ConfigMain& libdnf::getGlobalMainConfig()’:
/home/pokybuild/yocto-worker/buildtools/build/build/tmp/work/x86_64-linux/libdnf-native/0.38.1-r0/git/libdnf/dnf-context.cpp:2622:10: 
error: ‘cfgMainLoaded’ was not declared in this scope
      if (!cfgMainLoaded.test_and_set()) {
           ^
This was on a Centos 7 worker...

Ross