MDEV-25894: support AIX as a platform in mtr

Parital backport of 48938c57
so platform dependent AIX tests can be done.

mysql-test/include/platform.combinations

 [win]
 
+[aix]
+
 [unix]
 

mysql-test/lib/My/Platform.pm

@@ -22,7 +22,7 @@ use File::Basename;
 use File::Path;
 
 use base qw(Exporter);
-our @EXPORT= qw(IS_CYGWIN IS_WINDOWS IS_WIN32PERL
+our @EXPORT= qw(IS_CYGWIN IS_WINDOWS IS_WIN32PERL IS_AIX
 		native_path posix_path mixed_path
                 check_socket_path_length process_alive open_for_append);
 
@@ -54,6 +54,15 @@ BEGIN {
   }
 }
 
+BEGIN {
+  if ($^O eq "aix") {
+    eval 'sub IS_AIX { 1 }';
+  }
+  else {
+    eval 'sub IS_AIX { 0 }';
+  }
+}
+
 
 #
 # native_path

mysql-test/suite.pm

@@ -17,7 +17,13 @@ sub skip_combinations {
                 unless $ENV{DEBUG_KEY_MANAGEMENT_SO};
 
   # don't run tests for the wrong platform
-  $skip{'include/platform.combinations'} = [ (IS_WINDOWS) ? 'unix' : 'win' ];
+  if (IS_WINDOWS) {
+    $skip{'include/platform.combinations'} = [ 'aix', 'unix' ];
+  } elsif (IS_AIX) {
+    $skip{'include/platform.combinations'} = [ 'win', 'unix' ];
+  } else {
+    $skip{'include/platform.combinations'} = [ 'aix', 'win' ];
+  }
 
   $skip{'include/maybe_debug.combinations'} =
     [ defined $::mysqld_variables{'debug-dbug'} ? 'release' : 'debug' ];