fix BUILD_SHARED_LIBS and add it as an OPTION (cross fingers that CMake lets you expose existing vars as OPTION)

this should fix issue 176, thanks to Stephen Peters!

CMakeLists.txt

@@ -22,7 +22,7 @@ SET(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG")
 
 OPTION(USE_DOUBLE_PRECISION "Use double precision"	OFF)
 OPTION(USE_GRAPHICAL_BENCHMARK "Use Graphical Benchmark" ON)
-
+OPTION(BUILD_SHARED_LIBS "Use shared libraries" OFF)
 
 OPTION(USE_MSVC_RUNTIME_LIBRARY_DLL "Use MSVC Runtime Library DLL (/MD or /MDd)" OFF)
 OPTION(USE_MSVC_INCREMENTAL_LINKING "Use MSVC Incremental Linking" OFF)
@@ -226,6 +226,10 @@ ENDIF(USE_GLUT)
 	ENDIF()
 ENDIF(BUILD_BULLET2_DEMOS)
 
+IF (APPLE)
+  FIND_LIBRARY(COCOA_LIBRARY Cocoa)
+ENDIF()
+
 OPTION(BUILD_BULLET3 "Set when you want to build Bullet 3" ON)
 IF(BUILD_BULLET3)
 	OPTION(BUILD_BULLET3_DEMOS "Set when you want to build the Bullet 3 demos" ON)

btgui/OpenGLWindow/CMakeLists.txt

@@ -40,6 +40,8 @@ ENDIF()
 ADD_LIBRARY(OpenGLWindow ${OpenGLWindow_SRCS} ${OpenGLWindow_HDRS})
 if (UNIX AND NOT APPLE)
   target_link_libraries(OpenGLWindow X11)
+elseif (APPLE)
+  target_link_libraries(OpenGLWindow ${COCOA_LIBRARY})
 endif ()
 
 if (BUILD_SHARED_LIBS)