MDEV-30836 MTR Cygwin fix

Cygwin is more Unix-oriented. It does not treat \n as \r\n in regexps
(fixed by \R), it supplies Unix-style paths (fixed by
mixed_path()). It does some cleanup on paths when running exe, so it
will be different in exe output (like with $exe_mysqld, comparing
basename() is enough).

Cygwin installation

1. Just install latest perl version (only base package) and
   patchutils from cygwin-setup;
2. Don't forget to add c:\cygwin64\bin into system path
   before any other perl flavors;
3. There is path-style conflict (see below), you must replace
   c:\cygwin64\bin\sh.exe with the wrapper. Run MTR with
   --cygwin-subshell-fix=do for that. Make sure you are running Cygwin
   perl for the option to work.
4. Restart buildbot via net stop buildbot; net start buildbot

Path-style conflict of Cygwin-ish Perl

Some exe paths are passed to mysqltest which are executed by a native
call. This requires native-style paths (\-style). These exe paths also
executed by Perl itself. Either by MTR itself which is not so
critical, but also by tests' --perl blocks which is impossible to
change. And if Perl detects shell-expansion or uses pipe command it
passess this exe path to /bin/sh which is Cygwin-compiled bash that
cannot work with \-style (or at least in -c processing). Thus we require
\-style on some parts of MTR execution and /-style on another parts.

The examples of tests which cover these different parts are:

    main.mysqlbinlog_row_compressed \
    main.sp_trans_log

That could be great to force Perl to use something different from
/bin/sh, but unfortunately /bin/sh is compiled-in into binary. So the
only solution left is to overwrite /bin/sh with some wrapper script
which passes the command to cmd.exe instead of bash.

mysql-test/lib/My/Platform.pm

@@ -96,8 +96,13 @@ sub mixed_path {
 
 sub native_path {
   my ($path)= @_;
-  $path=~ s/\//\\/g
-    if (IS_CYGWIN or IS_WIN32PERL);
+  if (IS_CYGWIN) {
+    # \\\\ protects against 2 expansions (just for the case)
+    $path=~ s/\/+|\\+/\\\\\\\\/g;
+  }
+  elsif (IS_WINDOWS) {
+    $path=~ s/\/+/\\/g;
+  }
   return $path;
 }
 

mysql-test/mysql-test-run.pl

@@ -343,7 +343,7 @@ $| = 1; # Automatically flush STDOUT
 main();
 
 sub main {
-  $ENV{MTR_PERL}=$^X;
+  $ENV{MTR_PERL}= mixed_path($^X);
 
   # Default, verbosity on
   report_option('verbose', 0);
@@ -1758,11 +1758,12 @@ sub collect_mysqld_features {
   # to simplify the parsing, we'll merge all nicely formatted --help texts
   $list =~ s/\n {22}(\S)/ $1/g;
 
-  my @list= split '\n', $list;
+  my @list= split '\R', $list;
 
   $mysql_version_id= 0;
+  my $exe= basename($exe_mysqld);
   while (defined(my $line = shift @list)){
-     if ($line =~ /^\Q$exe_mysqld\E\s+Ver\s(\d+)\.(\d+)\.(\d+)(\S*)/ ) {
+     if ($line =~ /\W\Q$exe\E\s+Ver\s(\d+)\.(\d+)\.(\d+)(\S*)/ ) {
       $mysql_version_id= $1*10000 + $2*100 + $3;
       mtr_report("MariaDB Version $1.$2.$3$4");
       last;
@@ -1786,7 +1787,7 @@ sub collect_mysqld_features {
       next;
     }
 
-    last if /^$/; # then goes a list of variables, it ends with an empty line
+    last if /^\r?$/; # then goes a list of variables, it ends with an empty line
 
     # Put a variable into hash
     /^([\S]+)[ \t]+(.*?)\r?$/ or die "Could not parse mysqld --help: $_\n";
@@ -1817,7 +1818,7 @@ sub collect_mysqld_features_from_running_server ()
 
   my $list = `$cmd` or
     mtr_error("Could not connect to extern server using command: '$cmd'");
-  foreach my $line (split('\n', $list ))
+  foreach my $line (split('\R', $list ))
   {
     # Put variables into hash
     if ( $line =~ /^([\S]+)[ \t]+(.*?)\r?$/ )
@@ -2939,7 +2940,7 @@ sub initialize_servers {
 #
 sub sql_to_bootstrap {
   my ($sql) = @_;
-  my @lines= split(/\n/, $sql);
+  my @lines= split(/\R/, $sql);
   my $result= "\n";
   my $delimiter= ';';