Standard C++ 11 flag

[wacrenier]

Depending on your system, it may happen that cmake will not use the standard C++11 version causing many errors when compiling pn.cc (such as: 'char16_t' does not name a type).
Adding the "-std=gnu++11" flag to 'build/CMakeCache.txt' corrects the compiling errors but linking failed to find reference to libphonenumber library.
If adding the "-std=gnu++11 -ldl" flag to 'build/CMakeCache.txt' corrects all issues it implies non easy to find manual operation.

It would be great if we could add appropriate option directly in file 'CMakeList.txt' file.
Suggestion adding the 2 following lines in file 'CMakeList.txt':

SET(GCC_COVERAGE_COMPILE_FLAGS "-std=gnu++11 -ldl")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS}")

[camilleoudot]

Could not reproduce the issue so far. For the sake of clarity, maybe we could consider using CMake 3.1, which has a built in feature for specifying the C++ standard: https://cmake.org/cmake/help/latest/prop_tgt/CXX_STANDARD.html?