Fix missing ggml link in cmake for executables in examples on w64-mingw32

[marcom]

Without this I get linking errors on x86_64-w64-mingw32 (on linux I don't need this patch):

[01:33:38] [ 50%] Linking CXX executable ../../bin/main.exe
[01:33:38] cd /workspace/srcdir/llama.cpp/build/examples/main && /usr/bin/cmake -E cmake_link_script CMakeFiles/main.dir/link.txt --verbose=true
[01:33:38] /usr/bin/cmake -E rm -f CMakeFiles/main.dir/objects.a
[01:33:38] /opt/bin/x86_64-w64-mingw32-libgfortran5-cxx11/x86_64-w64-mingw32-ar qc CMakeFiles/main.dir/objects.a @CMakeFiles/main.dir/objects1.rsp
[01:33:38] /opt/bin/x86_64-w64-mingw32-libgfortran5-cxx11/x86_64-w64-mingw32-g++ --sysroot=/opt/x86_64-w64-mingw32/x86_64-w64-mingw32/sys-root/ -O3 -DNDEBUG -Wl,--whole-archive CMakeFiles/main.dir/objects.a -Wl,--no-whole-archive -o ../../bin/main.exe -Wl,--out-implib,libmain.dll.a -Wl,--major-image-version,0,--minor-image-version,0 @CMakeFiles/main.dir/linklibs.rsp
[01:33:38] /opt/x86_64-w64-mingw32/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/bin/ld: CMakeFiles/main.dir/objects.a(common.cpp.obj):common.cpp:(.text+0x4c8): undefined reference to `ggml_mlock_supported'
[01:33:38] collect2: error: ld returned 1 exit status

[anzz1]

FYI, conventional wisdom says you lose speed with mingw since gcc on windows isn't particularly awesome and msvc and clang generally produce better optimized code. then again, the codebase on this project is lean so I'm not sure to which extent the choice of compiler matters and it hasn't been thoroughly tested yet so ymmv. but just something to keep in mind .

[marcom]

Agreed. In this case though, I am trying to get llama.cpp to build in Julia's BinaryBuilder cross-compiling environment and have to use this setup for the Windows targets.