Mingw cross compilation (#24)

* Fixed icon filename capitalization

* Created mingw cmake toolchain

* Adjusted CMakeLists.txt for compatibility

* Small mingwcc.cmake cleanup

* Added cross-compilation instructions to readme

* Update README.md

Fixed typo

Co-authored-by: Nicola Orlando <nicolaorlando24@gmail.com>
Co-authored-by: Muzychenko Andrey <33288308+k4zmu2a@users.noreply.github.com>

mingwcc.cmake

@@ -0,0 +1,25 @@
+set(TOOLCHAIN_PREFIX "x86_64-w64-mingw32")
+
+set(CMAKE_SYSTEM_NAME Windows)
+
+set(CMAKE_CXX_COMPILER "${TOOLCHAIN_PREFIX}-g++")
+set(CMAKE_C_COMPILER "${TOOLCHAIN_PREFIX}-gcc")
+set(CMAKE_OBJCOPY "${TOOLCHAIN_PREFIX}-objcopy")
+set(CMAKE_STRIP "${TOOLCHAIN_PREFIX}-strip")
+set(CMAKE_SIZE "${TOOLCHAIN_PREFIX}-size")
+set(CMAKE_AR "${TOOLCHAIN_PREFIX}-ar")
+set(ASSEMBLER "${TOOLCHAIN_PREFIX}-as")
+
+
+set(CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PREFIX})
+
+# adjust the default behavior of the find commands:
+# search headers and libraries in the target environment
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY) 
+
+# search programs in the host environment
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+
+# Add the path to your toolchain version of SDL2
+set(SDL2_PATH /usr/${TOOLCHAIN_PREFIX})