Merge GDB 7.5.1

gdb/gnulib/import/memchr.valgrind

 # Suppress a valgrind message about use of uninitialized memory in memchr().
 # POSIX states that when the character is found, memchr must not read extra
 # bytes in an overestimated length (for example, where memchr is used to
 # implement strnlen).  However, we use a safe word read to provide a speedup.
 {
     memchr-value4
     Memcheck:Value4
     fun:rpl_memchr
 }
 {
     memchr-value8
     Memcheck:Value8
     fun:rpl_memchr
 }