g++ missing stddef.h

[slipbits]

g++ (GCC) 10.2.0
Win 7-64
Netbeans 12.5

g++ reported a compiler error in not finding stddef.h referenced in 
stdlib.h. I've looked in /usr/include and /usr/include/c++/v1. I found 
an stddef.h in /usr/include/c++/v1. Should I copy this to /usr/include?

The command being executed is 'c:\cygwin64\bin\g++.exe -std=c++11 -g -c 
NewCFile.cpp -o /dev/null'

I've checked my cygwin setup download options and have all of gcc 
modules included for C/C++. This is such an odd error that I feel I'm 
missing something, and I'm doing something wrong. Can someone help me 
fix this?

thanks
art

===== code =====

#include <stdlib.h>     /* exit, EXIT_FAILURE */

int main(int argc, char* argv[]) {
    exit (1);
}