Makefile: fix clang compilation
clang/clang++ can compile ublksrv sources, but it doesn't support
'-fcoroutines' flag, which is mandatory for older versions of g++ to
compile sources with c++20 coroutines support.
This commit changes Makefile.am and configure.ac, in such way, one can
build ublksrv sources using clang++.
After selecting c++ compiler, configure script will match $CXX with
clang++ or g++, flag -fcoroutines will be added to CXXFLAGS only when
building with g++. Order of match strings in AS_CASE is important,
because `*g++*` string includes `*clang++*`, thus we must check with
longer string first.
2 files changed
