tests: fix PATH problems on cygwin

* tests/misc/sort-compress: Remove non-portable over-restriction
of PATH; besides, commit 3ea177e changed sort to no longer default
to gzip.
* tests/rm/fail-eperm: Untaint, rather than clear, PATH.
* tests/misc/pwd-long: Likewise.  Also skip test if long path
cannot be created.
(normalize_to_cwd_relative): Use eq rather than ==, since cygwin
perl doesn't properly handle 64-bit ino_t numerically.

tests/misc/pwd-long

@@ -48,14 +48,19 @@ sub normalize_to_cwd_relative ($$$)
         and die "$ME: $dir does not contain old CWD\n";
       my $dir_prefix = $slash ? substr ($dir, 0, $slash) : '/';
       my ($d, $i) = (stat $dir_prefix)[0, 1];
-      $d == $dev && $i == $ino
+      $d eq $dev && $i eq $ino
         and return substr $dir, $slash + 1;
     }
 }
 
 # Set up a safe, well-known environment
-delete @ENV{qw(BASH_ENV CDPATH ENV PATH)};
+delete @ENV{qw(BASH_ENV CDPATH ENV)};
 $ENV{IFS}  = '';
+# PATH is tricky - we can't just clear it, or cygwin will fail.  But we
+# can't use it as-is, or taint checking in `` will stop us.  For this
+# script, it is enough to scrub the incoming $PATH first.
+$ENV{'PATH'} =~ /(.*)/;
+$ENV{'PATH'} = "$1";
 
 # Save CWD's device and inode numbers.
 my ($dev, $ino) = (stat '.')[0, 1];
@@ -70,9 +75,13 @@ substr ($expected, 0, 1) = '';
 my $i = 0;
 do
   {
-    mkdir $z, 0700
-      or die "$ME: at depth $i: $!\n";
-    chdir $z;
+    if (!mkdir $z, 0700)
+      {
+        warn "$ME: skipping this test; cannot create long directory name "
+          . "at depth $i: $!\n";
+        exit 77;
+      }
+    chdir $z
   }
 until (++$i == $n);
 
@@ -82,7 +91,7 @@ $abs_top_builddir
 my $build_src_dir = "$abs_top_builddir/src";
 if ($build_src_dir !~ m!^([-+.:/\w]+)$!)
   {
-    warn "$0: skipping this test; odd build source directory name:\n"
+    warn "$ME: skipping this test; odd build source directory name:\n"
       . "$build_src_dir\n";
     exit 77;
   }

tests/misc/sort-compress

@@ -32,7 +32,7 @@ TMPDIR=.; export TMPDIR
 
 fail=0
 
-# This should force the use of temp files compressed with the default gzip
+# This should force the use of temp files
 sort -S 1k in > out || fail=1
 compare exp out || fail=1
 
@@ -69,8 +69,4 @@ compare exp out || fail=1
 test -f ok || fail=1
 rm -f dzip ok
 
-# This is to make sure sort functions if it can't find the default gzip
-PATH=. "$SORT" -S 1k in > out || fail=1
-compare exp out || fail=1
-
 Exit $fail

tests/rm/fail-eperm

@@ -32,8 +32,13 @@ my $verbose = $ENV{VERBOSE} && $ENV{VERBOSE} eq 'yes';
 $ENV{LC_ALL} = 'C';
 
 # Set up a safe, well-known environment
-delete @ENV{qw(BASH_ENV CDPATH ENV PATH)};
+delete @ENV{qw(BASH_ENV CDPATH ENV)};
 $ENV{IFS}  = '';
+# PATH is tricky - we can't just clear it, or cygwin will fail.  But we
+# can't use it as-is, or taint checking in `` will stop us.  For this
+# script, it is enough to scrub the incoming $PATH first.
+$ENV{'PATH'} =~ /(.*)/;
+$ENV{'PATH'} = "$1";
 
 my @dir_list = qw(/tmp /var/tmp /usr/tmp);
 my $rm = "$ENV{abs_top_builddir}/src/rm";