• Press Windows + S, type PATH, and hit Enter
• Click Environment Variables..
• Navigate to System Variables, click Path to highlight.
• click Edit...

Default mingw path variable: C:\Program Files\mingw-w64\mingw64\bin
Default GNUstep path variable: C:\GNUstep\bin
Removed from Path variable temporarily since using GNUstep.

• If both GNUstep and mingw64 are added to the environment variable table, the terminal will use whichever is listed first in the table.
• Since mingw is a subset of GNUstep, path for GNUstep is listed before mingw64.

$ gcc -v
Using built-in specs.
COLLECT_GCC=C:\GNUstep\bin\gcc.exe
COLLECT_LTO_WRAPPER=c:/gnustep/bin/../libexec/gcc/mingw32/4.6.1/lto-wrapper.exe
Target: mingw32
Configured with: ../gcc-4.6.1/configure --enable-languages=c,c++,fortran,objc,obj-c++ --disable-sjlj-exceptions --with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry --enable-libstdcxx-debug --enable-version-specific-runtime-libs --build=mingw32 --prefix=/mingw
Thread model: win32
gcc version 4.6.1 (GCC)

Example: compile helloworld.m(source file) to hello.exe(executable)

gcc -I "C:\GNUstep\GNUstep\System\Library\Headers" -L "C:\GNUstep\GNUstep\System\Library\Libraries" -o hello helloWorld.m -lobjc -lgnustep-base -fconstant-string-class=NSConstantString  
./hello

<Foundation/Foundation.h> : C:\GNUstep\GNUstep\System\Library\Headers\Foundation
Libraries: C:\GNUstep\GNUstep\System\Library\Libraries

Online Objective-C Compiler