[gdb/testsuite] Fix gdb.base/style.exp with -m32

[gdb/testsuite] Fix gdb.base/style.exp with -m32

When running test-case gdb.base/style.exp with target board unix/-m32, we run
into (stripped styling from output, shortened file name):
...
(gdb) frame
    argv=0xffffc714) at src/gdb/testsuite/gdb.base/style.c:45
45        return some_called_function (); /* break here */
(gdb) FAIL: gdb.base/style.exp: frame when width=20
...
while with native we have instead:
...
(gdb) frame
    argv=0x7fffffffd478)
    at src/gdb/testsuite/gdb.base/style.c:45
45        return some_called_function (); /* break here */
(gdb) PASS: gdb.base/style.exp: frame when width=20
...

The problem is that due to argv having a different length for -m32, we get a
different layout, and the test-case doesn't accommodate for that.

Fix this by using a different regexp depending on the length of argv.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-01-14  Tom de Vries  <tdevries@suse.de>

	PR testsuite/24590
	* gdb.base/style.exp: Handle shorter argv in frame command output.