t9700: accommodate for Windows paths

Ever since fe53bbc (Git.pm: Always set Repository to absolute path
if autodetecting, 2009-05-07), the t9700 test _must_ fail on Windows
because of that age-old Unix paths vs Windows paths problem.

The underlying root cause is that Git cannot run with a regular Win32
variant of Perl, the assumption that every path is a Unix path is just
too strong in Git's Perl code.

As a consequence, Git for Windows is basically stuck with using the
MSYS2 variant of Perl which uses a POSIX emulation layer (which is a
friendly fork of Cygwin) _and_ a best-effort Unix <-> Windows paths
conversion whenever crossing the boundary between MSYS2 and regular
Win32 processes. It is best effort only, though, using heuristics to
automagically convert correctly in most cases, but not in all cases.

In the context of this here patch, this means that asking `git.exe` for
the absolute path of the `.git/` directory will return a Win32 path
because `git.exe` is a regular Win32 executable that has no idea about
Unix-ish paths. But above-mentioned commit introduced a test that wants
to verify that this path is identical to the one that the Git Perl
module reports (which refuses to use Win32 paths and uses Unix-ish paths
instead). Obviously, this must fail because no heuristics can kick in at
that layer.

This test failure has not even been caught when Git introduced Windows
support in its CI definition in 2e90484 (ci: add a Windows job to
the Azure Pipelines definition, 2019-01-29), as all tests relying on
Perl had to be disabled even from the start (because the CI runs would
otherwise have resulted in prohibitively long runtimes, not because
Windows is super slow per se, but because Git's test suite keeps
insisting on using technology that requires a POSIX emulation layer,
which _is_ super slow on Windows).

To work around this failure, let's use the `cygpath` utility to convert
the absolute `gitdir` path into the form that the Perl code expects.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

t/t9700/test.pl

@@ -117,7 +117,12 @@ sub adjust_dirsep {
 unlink $tmpfile;
 
 # paths
-is($r->repo_path, $abs_repo_dir . "/.git", "repo_path");
+my $abs_git_dir = $abs_repo_dir . "/.git";
+if ($^O eq 'msys' or $^O eq 'cygwin') {
+  $abs_git_dir = `cygpath -am "$abs_repo_dir/.git"`;
+  $abs_git_dir =~ s/\r?\n?$//;
+}
+is($r->repo_path, $abs_git_dir, "repo_path");
 is($r->wc_path, $abs_repo_dir . "/", "wc_path");
 is($r->wc_subdir, "", "wc_subdir initial");
 $r->wc_chdir("directory1");
@@ -127,7 +132,7 @@ sub adjust_dirsep {
 # Object generation in sub directory
 chdir("directory2");
 my $r2 = Git->repository();
-is($r2->repo_path, $abs_repo_dir . "/.git", "repo_path (2)");
+is($r2->repo_path, $abs_git_dir, "repo_path (2)");
 is($r2->wc_path, $abs_repo_dir . "/", "wc_path (2)");
 is($r2->wc_subdir, "directory2/", "wc_subdir initial (2)");