btrfs-progs: compilation errors when using musl libc

- limits.h must be included to pick up PATH_MAX.
- remove double declaration of BTRFS_DISABLE_BACKTRACE

kerncompat.h assumed that if __GLIBC__ was not defined,
it could safely define BTRFS_DISABLE_BACKTRACE, however this can be
defined by the configure script. Added a check to ensure it is not
defined first.

Signed-off-by: Brendan Heading <brendanheading@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

cmds-inspect.c

@@ -21,6 +21,7 @@
 #include <sys/ioctl.h>
 #include <errno.h>
 #include <getopt.h>
+#include <limits.h>
 
 #include "kerncompat.h"
 #include "ioctl.h"

cmds-receive.c

@@ -28,6 +28,7 @@
 #include <wait.h>
 #include <assert.h>
 #include <getopt.h>
+#include <limits.h>
 
 #include <sys/stat.h>
 #include <sys/types.h>

cmds-scrub.c

@@ -34,6 +34,7 @@
 #include <ctype.h>
 #include <signal.h>
 #include <stdarg.h>
+#include <limits.h>
 
 #include "ctree.h"
 #include "ioctl.h"

cmds-send.c

@@ -33,6 +33,7 @@
 #include <assert.h>
 #include <getopt.h>
 #include <uuid/uuid.h>
+#include <limits.h>
 
 #include "ctree.h"
 #include "ioctl.h"

kerncompat.h

@@ -33,7 +33,9 @@
 #include <features.h>
 
 #ifndef __GLIBC__
+#ifndef BTRFS_DISABLE_BACKTRACE
 #define BTRFS_DISABLE_BACKTRACE
+#endif
 #define __always_inline __inline __attribute__ ((__always_inline__))
 #endif