Go through both run_make_tests.pl and test_driver.pl and slightly
modernize the Perl and clean up indentation etc. Fix a number of
warnings in the test scripts detected by running with -w.
* tests/test_driver.pl: Move make error string detection out of the
base test driver.
(run_all_tests): Ensure that we always look for tests in the cwd.
* tests/run_make_tests.pl: Use File::Spec for path manipulations.
Correctly use setlocale() when detecting error strings.
Get configuration from the config-flags.pm file not config.status.
* tests/scripts/features/archives: Use new $cwddir variable.
* tests/scripts/features/reinvoke: Add missing semicolon.
* tests/scripts/features/vpath2: Avoid non-existent variable.
* tests/scripts/functions/foreach: Escape variables.
* tests/scripts/misc/bs-nl: Remove non-existing \v escape sequence.
* tests/scripts/misc/general4: Use handy create_file().
* tests/scripts/options/dash-C: Use Cwd/$cwddir.
* tests/scripts/options/dash-I: Use subst_make_string() and #PWD#.
* tests/scripts/options/symlinks: Use File::Spec.
* tests/scripts/targets/DEFAULT: Use create_file and run_make_test.
* tests/scripts/variables/CURDIR: Use run_make_test.
* tests/scripts/variables/automatic: Remove extraneous "\".
* tests/scripts/vms/library: Remove extra "my" and extraneous "\".
