*: mass renaming of USE_XXXX to IF_XXXX

and SKIP_XXXX to IF_NOT_XXXX - the second one was especially
badly named. It was not skipping anything!

libbb/mtab_file.c

@@ -12,4 +12,4 @@
 /* Busybox mount uses either /proc/mounts or /etc/mtab to
  * get the list of currently mounted filesystems */
 const char bb_path_mtab_file[] ALIGN1 =
-USE_FEATURE_MTAB_SUPPORT("/etc/mtab")SKIP_FEATURE_MTAB_SUPPORT("/proc/mounts");
+IF_FEATURE_MTAB_SUPPORT("/etc/mtab")IF_NOT_FEATURE_MTAB_SUPPORT("/proc/mounts");