Updating CMake (seems to have) broke my program

I updated from CMake 3.6 to whatever the latest version is (3.12.0-rc2) and now one of my programs won't compile.

The weird thing is, the error message shows undefined symbols from in the standard library itself. Here's the error message:

Undefined symbols for architecture x86_64:
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string(char const*)", referenced from:
      GetName() in ncc.cpp.o
      Expression() in ncc.cpp.o
      Term() in ncc.cpp.o
      GetNum() in ncc.cpp.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string()", referenced from:
      GetName() in ncc.cpp.o
      GetNum() in ncc.cpp.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::operator+=(char)", referenced from:
      GetName() in ncc.cpp.o
      GetNum() in ncc.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [ncc] Error 1
make[1]: *** [CMakeFiles/ncc.dir/all] Error 2
make: *** [all] Error 2

How do I fix this? Do I need to link to a different version of the standard library? And if so, how I tell CMake that?

Here's my CMakeLists.txt file:

cmake_minimum_required(VERSION 3.0)

project(ncc)

add_definitions(-std=c++14)

add_subdirectory(${CMAKE_SOURCE_DIR}/src/)

add_executable(ncc ${CompSource})
add_executable(ncc-opt ${OptSource})
add_executable(nci ${IntSource})

I tried it with the add_definitions line and without it, which didn't seem to make a difference.

This is the relevant output from running make VERBOSE=1:

Scanning dependencies of target ncc
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/ncc.dir/build.make CMakeFiles/ncc.dir/build
[ 83%] Building CXX object CMakeFiles/ncc.dir/src/ncc.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++    -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk   -std=c++14 -o CMakeFiles/ncc.dir/src/ncc.cpp.o -c /Users/nepps/Dropbox/Projects/ncc/src/ncc.cpp
[100%] Linking CXX executable ncc
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/ncc.dir/link.txt --verbose=1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names  CMakeFiles/ncc.dir/src/ncc.cpp.o  -o ncc 
Undefined symbols for architecture x86_64:
(same errors as above)

Feel free to comment if you need more information. I'm using a MacBook pro running MacOS 10.13.3.

Well, I'm not sure why it worked, but all of the functions in the program were marked static and removing that made the errors go away. Go figure.