[gdb/testsuite] Fix gdb.base/break-interp.exp with check-read1

When running test-case gdb.base/break-interp.exp with check-read1, I run into:
...
(gdb) info files^M
  ...
	0x00007ffff7e75980 - 0x00007ffff7e796a0 @ 0x001f1970 is .bss in /data/vries/gdb/leap-15-5/build/gdb/testsuite/outputs/gdb.base/break-interp/break-interp-BINprelinkNOdebugNOFAIL: gdb.base/break-interp.exp: ldprelink=NO: ldsepdebug=NO: binprelink=NO: binsepdebug=NO: binpie=NO: INNER: symbol-less: info files (timeout)
pieNO.d/libc.so.6^M
...

The code has two adaptations to deal with the large output:
- nested gdb_test_multiple, and
- an exp_continue in the inner gdb_test_multiple.

The former seems unnecessary, and the latter doesn't trigger often enough
because of an incomplete hex number regexp, causing the timeout.

Get rid of both of these, and use -lbl instead.

Tested on x86_64-linux.
1 file changed