[gdb/testsuite] Fix duplicate in gdb.base/info-macros.exp

[gdb/testsuite] Fix duplicate in gdb.base/info-macros.exp

When running test-case gdb.base/info-macros.exp, I run into:
...
PASS: gdb.base/info-macros.exp: info macro --
PASS: gdb.base/info-macros.exp: info macro --
DUPLICATE: gdb.base/info-macros.exp: info macro --
PASS: gdb.base/info-macros.exp: info macro  --
...

These messages come from gdb_test calls using the following commands:
- "info macro --"
- "info macro -- "
- "info macro  -- ".

Apparantly the test names get stripped of trailing whitespace, and the first
two end up identical.

Fix this by explicitly specifying an <EOL> after the trailing whitespace in
the test name, such that we have:
...
PASS: gdb.base/info-macros.exp: info macro --
PASS: gdb.base/info-macros.exp: info macro -- <EOL>
PASS: gdb.base/info-macros.exp: info macro  -- <EOL>
...

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-06-24  Tom de Vries  <tdevries@suse.de>

	* gdb.base/info-macros.exp: Add <EOL> after trailing whitespace in
	test names.