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

libexec/ld.elf_so/diagassert.c

@@ -0,0 +1,9 @@
+#include <assert.h>
+#include <stdlib.h>
+
+__dead void
+/*ARGSUSED*/
+__diagassert13(const char *fn, int fl, const char *fu, const char *m)
+{
+	abort();
+}