Fix logger signed unsigned error with GCC 7.3 in Cygwin (#10009)

src/modules/logger/logger.cpp

@@ -64,13 +64,15 @@
 #include <replay/definitions.hpp>
 #include <version/version.h>
 
-#ifdef __PX4_DARWIN
+#if defined(__PX4_DARWIN)
 #include <sys/param.h>
 #include <sys/mount.h>
 #else
 #include <sys/statfs.h>
 #endif
 
+typedef decltype(statfs::f_bavail) px4_statfs_buf_f_bavail_t;
+
 #define GPS_EPOCH_SECS ((time_t)1234567890ULL)
 
 //#define DBGPRINT //write status output every few seconds