gdb/testsuite: Reduce test name duplication in gdb.base tests

This commit removes some, but not all, of the test name duplication
within the gdb.base tests.  On my local machine this takes the number
of duplicate test names in this set of tests from 454 to 145.  It is
possible that different setups might encounter more duplicate tests.

gdb/testsuite/ChangeLog:

	* gdb.base/break-interp.exp: Reduce test name duplication.
	* gdb.base/call-sc.exp: Likewise.
	* gdb.base/callfuncs.exp: Likewise.
	* gdb.base/charset.exp: Likewise.
	* gdb.base/dump.exp: Likewise.
	* gdb.base/ena-dis-br.exp: Likewise.
	* gdb.base/relational.exp: Likewise.
	* gdb.base/step-over-syscall.exp: Likewise.
	* gdb.base/structs.exp: Likewise.