Rearrange the test a bit to make the separation a bit clearer, also try snuggling crates up a bit closer to other things.
file(GLOB lua_src *.c *.h)
set(LIBRARY_OUTPUT_PATH ${EXECUTABLE_OUTPUT_PATH})
IF(APPLE)
set(CMAKE_OSX_ARCHITECTURES "x86_64;i386;ppc7400")
set(build_type STATIC)
add_definitions(-DLUA_USE_LINUX)
ENDIF(APPLE)
IF(WIN32)
set(build_type SHARED)
add_definitions(-DLUA_BUILD_AS_DLL)
ENDIF(WIN32)
add_library (lua ${build_type} ${lua_src})
if(WIN32)
SET_TARGET_PROPERTIES(lua PROPERTIES PREFIX "")
install(TARGETS lua DESTINATION ${target_dir})
endif(WIN32)