[gdb/testsuite] Add nopie to gdb.base/eh_return.exp

[gdb/testsuite] Add nopie to gdb.base/eh_return.exp

When running test-case gdb.base/eh_return.exp with target board
unix/-fPIE/-pie, we run into:
...
(gdb) break *0x88e^M
Breakpoint 1 at 0x88e: file eh_return.c, line 54.^M
(gdb) PASS: gdb.base/eh_return.exp: setting breakpoint at *0x88e
run ^M
Starting program: eh_return ^M
Warning:^M
Cannot insert breakpoint 1.^M
Cannot access memory at address 0x88e^M
^M
(gdb) FAIL: gdb.base/eh_return.exp: hit breakpoint
...

The problem is that gdb does not support setting breakpoints on unrelocated
addresses.

Fix this by using nopie for the test-case.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-08-31  Tom de Vries  <tdevries@suse.de>

	* gdb.base/eh_return.exp: Use nopie.