Prepare for Android NDK build

Modify CMakeList.txt prepare for Android NDK build

Signed-off-by: AuroraRAS <chplee@gmail.com>

platforms/posix/CMakeLists.txt

@@ -33,7 +33,7 @@ add_executable(px4
 target_link_libraries(px4
 	PRIVATE
 		${module_libraries}
-		pthread m
+		m
 
 		# horrible circular dependencies that need to be teased apart
 		px4_layer px4_platform
@@ -41,10 +41,14 @@ target_link_libraries(px4
 		parameters
 )
 
-if(NOT APPLE)
+if((NOT APPLE) AND (NOT ANDROID))
 	target_link_libraries(px4 PRIVATE rt)
 endif()
 
+if(NOT ANDROID)
+	target_link_libraries(px4 PRIVATE pthread)
+endif()
+
 target_link_libraries(px4 PRIVATE uORB)
 
 #=============================================================================