gdb/testsuite: link some dwarf2 tests with nopie

gdb/testsuite: link some dwarf2 tests with nopie

I noticed some gdb.dwarf2 tests not running on my machine because of
this:

    Running /home/simark/src/binutils-gdb/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.exp ...
    gdb compile failed, /usr/bin/ld: /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.dwarf2/dw2-single-line-discriminators/dw2-single-line-discriminators0.o: relocation R_X86_64_32S against
     symbol `x' can not be used when making a PIE object; recompile with -fPIE
    collect2: error: ld returned 1 exit status

We get this when the target toolchain produces position-independent
executables by default.  These tests are built from some assembly which
produces some relocations incompatible with position-independent
executables.

Add `nopie` to the compilation flags of these tests to force the
toolchain to produce non-position-independent executables.  With this,
the changed tests run successfully on my machine.

gdb/ChangeLog:

	* gdb.dwarf2/clztest.exp, gdb.dwarf2/dw2-common-block.exp,
	gdb.dwarf2/dw2-dup-frame.exp, gdb.dwarf2/dw2-reg-undefined.exp,
	gdb.dwarf2/dw2-single-line-discriminators.exp,
	dw2-undefined-ret-addr.exp: Pass nopie to compilation options.

Change-Id: Ie06c946f8e56a6030be247d1c57f416fa8b67e4c