gdb.base/memattr.exp regexp improvements.

  https://sourceware.org/ml/gdb-patches/2014-04/msg00210.html

Improve the regexp used in the memattr.exp test so allow for different
memory regions (.data / .bss) being laid out in different orders.

gdb/testsuite/ChangeLog:

	* gdb.base/memattr.exp: Improve regexps to handle memory regions
	appearing in any order.