cmake toolchain file for mingw-w64 x86_64 builds on Ubuntu

mingw-w64-x86_64.cmake

# Sample toolchain file for building for Windows from an Ubuntu Linux system.
#
# Typical usage:
#    *) install cross compiler: `sudo apt-get install mingw-w64` or `brew install mingw-w64` on macOS
#    *) cmake -DCMAKE_TOOLCHAIN_FILE=~/mingw-w64-x86_64.cmake -G Ninja -B build -S .
#    *) ninja -C build


set(CMAKE_SYSTEM_NAME Windows)
set(TOOLCHAIN_PREFIX x86_64-w64-mingw32)

# cross compilers to use for C, C++ and Fortran
set(CMAKE_C_COMPILER ${TOOLCHAIN_PREFIX}-gcc)
set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PREFIX}-g++)
set(CMAKE_Fortran_COMPILER ${TOOLCHAIN_PREFIX}-gfortran)
set(CMAKE_RC_COMPILER ${TOOLCHAIN_PREFIX}-windres)

# target environment on the build host system
set(CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PREFIX})

# modify default behavior of FIND_XXX() commands
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -static -Os")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static -Os")