[gdb/testsuite] Add nopie to gdb.base/unwind-on-each-insn-amd64-2.exp
When running test-case gdb.base/unwind-on-each-insn-amd64-2.exp with target
board unix/-fPIE/-pie, I run into:
...
gdb compile failed, ld: unwind-on-each-insn-amd64-21.o: relocation \
R_X86_64_32S against `.text' can not be used when making a PIE object; \
recompile with -fPIE
ld: failed to set dynamic section sizes: bad value
...
Fix this by hardcoding nopie in the test-case, and for good measure in the
other test-cases that source unwind-on-each-insn.exp.tcl and use a .s file.
Tested on x86_64-linux.
Approved-by: Kevin Buettner <kevinb@redhat.com>