load_mon: get mem_usage by reading /proc/meminfo on Linux

src/modules/load_mon/LoadMon.hpp

@@ -33,7 +33,9 @@
 
 #pragma once
 
+#if defined(__PX4_NUTTX)
 #include <malloc.h>
+#endif
 #include <drivers/drv_hrt.h>
 #include <lib/perf/perf_counter.h>
 #include <px4_platform_common/px4_config.h>
@@ -48,7 +50,6 @@
 
 #if defined(__PX4_LINUX)
 #include <sys/times.h>
-#include <malloc.h>
 #endif
 
 namespace load_mon
@@ -92,6 +93,7 @@ private:
 	uORB::Publication<cpuload_s> _cpuload_pub {ORB_ID(cpuload)};
 
 #if defined(__PX4_LINUX)
+	FILE *_proc_fd = nullptr;
 	/* calculate usage directly from clock ticks on Linux */
 	clock_t _last_total_time_stamp{};
 	clock_t _last_spent_time_stamp{};