build: add freebsd support (#4049)

cmake/compile_definitions/linux.cmake

@@ -1,6 +1,10 @@
 # linux specific compile definitions
 
-add_compile_definitions(SUNSHINE_PLATFORM="linux")
+if(FREEBSD)
+    add_compile_definitions(SUNSHINE_PLATFORM="freebsd")
+else()
+    add_compile_definitions(SUNSHINE_PLATFORM="linux")
+endif()
 
 # AppImage
 if(${SUNSHINE_BUILD_APPIMAGE})
@@ -211,6 +215,9 @@ endif()
 # These need to be set before adding the inputtino subdirectory in order for them to be picked up
 set(LIBEVDEV_CUSTOM_INCLUDE_DIR "${EVDEV_INCLUDE_DIR}")
 set(LIBEVDEV_CUSTOM_LIBRARY "${EVDEV_LIBRARY}")
+if(FREEBSD)
+    set(USE_UHID OFF)
+endif()
 
 add_subdirectory("${CMAKE_SOURCE_DIR}/third-party/inputtino")
 list(APPEND SUNSHINE_EXTERNAL_LIBRARIES inputtino::libinputtino)