MTR flag to mark tests as incompatible with macOS

Introduces a new MTR include, not_mac.inc, which when included
at the top of a test, prevents that test from running on macOS.

mysql-test/include/not_mac.inc

+#
+# suite.pm will make sure that all tests including this file
+# will be skipped if run under macOS
+#

mysql-test/lib/My/Platform.pm

@@ -23,7 +23,7 @@ use File::Path;
 use Carp;
 
 use base qw(Exporter);
-our @EXPORT= qw(IS_CYGWIN IS_MSYS IS_WINDOWS IS_WIN32PERL IS_AIX
+our @EXPORT= qw(IS_CYGWIN IS_MSYS IS_WINDOWS IS_WIN32PERL IS_AIX IS_MAC
 		native_path posix_path mixed_path
                 check_socket_path_length process_alive open_for_append);
 
@@ -70,6 +70,14 @@ BEGIN {
   }
 }
 
+BEGIN {
+  if ($^O eq "darwin") {
+    eval 'sub IS_MAC { 1 }';
+  }
+  else {
+    eval 'sub IS_MAC { 0 }';
+  }
+}
 
 #
 # native_path

mysql-test/main/json_normalize.test

+# Test doesn't work on macOS.
+--source include/not_mac.inc
+
 set names utf8;
 
 create table t1 (json json);

mysql-test/suite.pm

@@ -56,7 +56,7 @@ sub skip_combinations {
 
   $skip{'include/not_windows.inc'} = 'Requires not Windows' if IS_WINDOWS;
   $skip{'include/not_aix.inc'} = 'Requires not AIX' if IS_AIX;
-
+  $skip{'include/not_mac.inc'} = 'Requires not macOS' if IS_MAC;
   $skip{'main/plugin_loaderr.test'} = 'needs compiled-in innodb'
             unless $::mysqld_variables{'innodb'} eq "ON";