Libraries updates and cleanup

* Updating common/lib
 * Updating lib/csu
 * Updating lib/libc
 * Updating libexec/ld.elf_so
 * Corrected test on __minix in featuretest to actually follow the
   meaning of the comment.
 * Cleaned up _REENTRANT-related defintions.
 * Disabled -D_REENTRANT for libfetch
 * Removing some unneeded __NBSD_LIBC defines and tests

Change-Id: Ic1394baef74d11b9f86b312f5ff4bbc3cbf72ce2

usr.sbin/installboot/install_master.c

@@ -16,6 +16,8 @@
 #include <dirent.h>
 #include <sys/stat.h>
 
+#include "installboot.h"
+
 #define BOOTBLOCK	0	/* Of course */
 #define BOOT_BLOCK_SIZE 1024
 #define SIGNATURE	0xAA55	/* Boot block signature. */

usr.sbin/installboot/minixfs3.c

@@ -8,6 +8,8 @@
 #include <unistd.h>
 #include <string.h>
 
+#include "installboot.h"
+
 #ifndef DFL_SECSIZE
 #define DFL_SECSIZE     512
 #endif