gdb/testsuite: Disable path and duplicate checks when parallel testing

gdb/testsuite: Disable path and duplicate checks when parallel testing

This commit disables the recently added checking for paths in test
names, and for duplicate test names, when the gdb tests are run in
parallel.

When running the gdb tests in parallel the extra result count lines
produced cause the dg-extract-results scripts to exit with an error.

The patches for the dg-extract-results scripts have been posted to the
gcc-patches mailing list here:

https://gcc.gnu.org/pipermail/gcc-patches/2020-May/545562.html

Once they are merged there then these changes can be merged over to
binutils-gdb, and this commit can be reverted.

gdb/testsuite/ChangeLog:

	* lib/check-test-names.exp: Disable when testing is being run in
	parallel.