Included <paths.h> where useful in fuse-lite

Both fusermount.c and mount_util.c use _PATH_MOUNTED, so they should
include <paths.h>, which provides this definition.
This is required for building with the musl C library.

Contributed by Thomas Petazzoni

libfuse-lite/fusermount.c

@@ -19,6 +19,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <pwd.h>
+#include <paths.h>
 
 #ifdef __SOLARIS__
 #include <sys/mnttab.h>

libfuse-lite/mount_util.c

@@ -15,6 +15,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <limits.h>
+#include <paths.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
 #ifdef __SOLARIS__