[common] move spinlock to pure header def (#3287)

inline justified because it's like 4-5 assembly instructions max

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3287
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/common/CMakeLists.txt

@@ -120,7 +120,6 @@ add_library(
   settings_setting.h
   slot_vector.h
   socket_types.h
-  spin_lock.cpp
   spin_lock.h
   stb.cpp
   stb.h