int x definition, GLOBAL_VARIABLE_PREDECLARATION and tkDecls.h on MacOS

Create a new project, with this main.cpp

int x = 1;

int main() {
    return 0;
}

then follow the definition/declaration gutter icon:

This takes you to

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/tkDecls.h line 62:

Of course it compiles and runs correctly, but this is a bit weird.

Clion build CL-193.5233.103 on MacOS Mojave 10.14.6 (18G103).