[build] Only add SIMU_AUDIO option if SDL was found, and turn it ON b…

…y default. (opentx#4248)

radio/src/CMakeLists.txt

@@ -29,7 +29,9 @@ option(AUTOSOURCE "Automatic source detection in menus" ON)
 option(AUTOSWITCH "Automatic switch detection in menus" ON)
 option(JITTER_MEASURE "Enable ADC jitter measurement" OFF)
 option(WATCHDOG_DISABLED "Disable hardware Watchdog" OFF)
-option(SIMU_AUDIO "Enable simulator audio" OFF)
+if(SDL_FOUND)
+  option(SIMU_AUDIO "Enable simulator audio." ON)
+endif()
 option(SIMU_DISKIO "Enable disk IO simulation in simulator. Simulator will use FatFs module and simulated IO layer that  uses \"./sdcard.image\" file as image of SD card. This file must contain whole SD card from first to last sector" OFF)
 option(SIMU_LUA_COMPILER "Pre-compile and save Lua scripts in simulator." ON)
 option(FAS_PROTOTYPE "Support of old FAS prototypes (different resistors)" OFF)
@@ -470,7 +472,7 @@ if(NOT MSVC)
 
     set(CMAKE_C_COMPILER avr-gcc)
     set(CMAKE_CXX_COMPILER avr-gcc)
-    
+
     set(COMMON_FLAGS "-mmcu=${MCU} -DF_CPU=16000000UL -O${OPT} -gdwarf-2 -fno-exceptions -flto -fwhole-program -fno-inline-small-functions -mstrict-X ${WARNING_FLAGS}")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${COMMON_FLAGS}")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMMON_FLAGS}")