fix(build): fix compilation error on MacOS for C++14

[empiredan]

#1647

The standard followed by v2.5
would be C++14. However, Compilation on MacOS failed due to some errors, such as:

• no member named 'make_unique' in namespace 'std'
• initialized lambda captures are a C++14 extension
• 'ext/alloc_traits.h' file not found

Most of the errors are about C++14. cmake directives should be fixed to make C++14
compilation on MacOS work well.

[empiredan]

#include <ext/alloc_traits.h> should be declared as no_include with IWYU due to following compilation error on MacOS:

[ 43%] Building CXX object src/meta/CMakeFiles/dsn_meta_server.dir/meta_service_app.cpp.o
/Users/runner/work/incubator-pegasus/incubator-pegasus/src/meta/meta_service.cpp:29:10: fatal error: 'ext/alloc_traits.h' file not found
#include <ext/alloc_traits.h>
         ^~~~~~~~~~~~~~~~~~~~
1 error generated.
make[2]: *** [src/meta/CMakeFiles/dsn_meta_server.dir/meta_service.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....

[empiredan]

Use target_compile_features by referring to the following docs:

• https://stackoverflow.com/questions/40452287/let-cmake-with-clang-use-c11-c14
• https://stackoverflow.com/questions/41220265/check-if-a-c11-feature-is-enabled-in-compiler-with-cmake/41221098#41221098
• https://cmake.org/cmake/help/latest/manual/cmake-compile-features.7.html