Fixes for AutoFDO testing

Fixes for AutoFDO testing

* create_gcov tool doesn't currently support dwarf 5 so I made a change in profopt.exp
  to pass -gdwarf-4 when compiling the binary to profile.

* I updated the invocation of create_gcov in profopt.exp to pass -gcov_version=2.
  I recently made a change to create_gcov to support version 2:
  https://github.com/google/autofdo/pull/117 .

* I removed useless -o perf.data from the invocation of gcc-auto-profile in
  target-supports.exp.

These changes contribute to fixing PR gcov-profile/71672.

gcc/testsuite/ChangeLog:

	* lib/profopt.exp: Pass gdwarf-4 when compiling test to profile; pass -gcov_version=2.
	* lib/target-supports.exp: Remove unnecessary -o perf.data passed to gcc-auto-profile.