[gdb/testsuite] Add nopie in two test-cases

[gdb/testsuite] Add nopie in two test-cases

When running test-case gdb.dwarf2/dw2-restrict.exp on openSUSE Leap 15.2 with
gcc-PIE installed (switching compiler default to -fPIE/-pie), I get:
...
gdb compile failed, ld: outputs/gdb.dwarf2/dw2-restrict/dw2-restrict0.o: \
  warning: relocation in read-only section `.text'
ld: warning: creating DT_TEXTREL in a PIE
UNTESTED: gdb.dwarf2/dw2-restrict.exp: failed to prepare
...

This is due to using a hardcoded .S file that was generated with -fno-PIE.

Fix this by adding the missing nopie.

Likewise in gdb.arch/amd64-tailcall-noret.exp.

Tested on x86_64-linux.