deps: no /safeseh for ml64.exe

`ml64.exe` doesn't support `/safeseh` option. Do not attempt to use it
if `target_arch=="x64"`.

See: https://msdn.microsoft.com/en-us/library/s0ksfwcf.aspx

deps/openssl/openssl.gyp

@@ -121,15 +121,17 @@
         }], # end of conditions of openssl_no_asm
         ['OS=="win"', {
           'defines' : ['<@(openssl_defines_all_win)'],
+        }, {
+          'defines' : ['<@(openssl_defines_all_non_win)']
+        }],
+        ['target_arch=="ia32" and OS=="win"', {
           'msvs_settings': {
             'MASM': {
               # Use /safeseh, see commit: 01fa5ee
               'UseSafeExceptionHandlers': 'true',
             },
           },
-        }, {
-          'defines' : ['<@(openssl_defines_all_non_win)']
-        }]
+        }],
       ],
       'include_dirs': ['<@(openssl_include_dirs)'],
       'direct_dependent_settings': {