cmake: only optimize for size on NuttX

With this change only builds for NuttX which are very much flash size
constraint are optimized for size. All other builds (e.g. SITL,
Snapdragon, etc.) are left at the default for debugging or -O2 for the
usual use.

cmake/common/px4_base.cmake

@@ -675,7 +675,9 @@ function(px4_add_common_flags)
 
 	if ($ENV{MEMORY_DEBUG} MATCHES "1")
 		message(STATUS "address sanitizer enabled")
-		set(max_optimization -Os)
+		if ("${OS}" STREQUAL "nuttx")
+			set(max_optimization -Os)
+		endif()
 
 		# Do not use optimization_flags (without _) as that is already used.
 		set(_optimization_flags
@@ -687,7 +689,11 @@ function(px4_add_common_flags)
 			-g3 -fsanitize=address
 			)
 	else()
-		set(max_optimization -Os)
+		if ("${OS}" STREQUAL "nuttx")
+			set(max_optimization -Os)
+		else()
+			set(max_optimization -O2)
+		endif()
 
 		if ("${OS}" STREQUAL "qurt")
 			set(PIC_FLAG -fPIC)