fix: make USE_OPENGL compile definitions conditional

The USE_OPENGL compile definition was being added unconditionally to the client
and main executable targets, even when USE_OPENGL option was set to OFF. This
could cause incorrect code paths to be enabled at compile time.

Changes:
- Make client target USE_OPENGL definition conditional: $<$<BOOL:>:USE_OPENGL>
- Make main executable USE_OPENGL definition conditional: $<$<BOOL:>:USE_OPENGL>

This ensures that when USE_OPENGL=OFF, the USE_OPENGL preprocessor definition
is not set, preventing compilation of OpenGL-specific code paths.

Author: timfox

CMakeLists.txt

@@ -1853,7 +1853,7 @@ TARGET_INCLUDE_DIRECTORIES(client PRIVATE src/client/mp3)
 message(STATUS "MP3 support enabled with custom mp3")
 
 # Define renderer flags for client
-TARGET_COMPILE_DEFINITIONS(client PRIVATE USE_OPENGL USE_VULKAN USE_SDL)
+TARGET_COMPILE_DEFINITIONS(client PRIVATE $<$<BOOL:${USE_OPENGL}>:USE_OPENGL> USE_VULKAN USE_SDL)
 
 IF(USE_CIMGUI AND DEFINED CIMGUI_DIR)
 	set(CIMGUI_USER_CONFIG "\"cimconfig.h\"")
@@ -3276,7 +3276,7 @@ ENDIF()
 TARGET_LINK_LIBRARIES(${CNAME}${BINEXT} PRIVATE botlib client common q3ui GL)
 TARGET_LINK_OPTIONS(${CNAME}${BINEXT} PRIVATE -Wl,--export-dynamic)
 TARGET_INCLUDE_DIRECTORIES(${CNAME}${BINEXT} PRIVATE src/common src)
-TARGET_COMPILE_DEFINITIONS(${CNAME}${BINEXT} PRIVATE USE_OPENGL)
+TARGET_COMPILE_DEFINITIONS(${CNAME}${BINEXT} PRIVATE $<$<BOOL:${USE_OPENGL}>:USE_OPENGL>)
 IF(USE_UI2)
 	TARGET_LINK_LIBRARIES(${CNAME}${BINEXT} PRIVATE ui2)
 ENDIF()