d: Don't create gdc.test symlink in the gdc testsuite directory

d: Don't create gdc.test symlink in the gdc testsuite directory

Instead, tests are copied from the source tree (i.e: $srcdir/compilable)
into the test base directory ($base_dir/compilable).   A dejagnu test
file with all translated test directives is created in a path that
follows DejaGnu naming conventions ($base_dir/gdc.test/compilable),
which is then passed to `dg-test'.

Before invoking the compiler, the gdc.test prefixed is trimmed from the
test program in `gdc-dg-test' so that all copied test files are picked
up with the correct path names.

gcc/testsuite/ChangeLog:

	* lib/gdc-utils.exp (gdc-copy-extra): Rename to...
	(gdc-copy-file): ... this.  Use file copy instead of open/close.
	(gdc-convert-test): Save translated dejagnu test to gdc.test
	directory, only write dejagnu directives to the test file.
	(gdc-do-test): Don't create gdc.test symlink.