Reland "msvs/ninja win: Fix support for ImageHasSafeExceptionHandlers"

pylib/gyp/msvs_emulation.py

Index: pylib/gyp/msvs_emulation.py
diff --git a/pylib/gyp/msvs_emulation.py b/pylib/gyp/msvs_emulation.py
index 050e95c2c569ffeee49efc2e27efa94d790cac13..ce5c46ea5b3d9501669c0d028062399344c602c4 100644
--- a/pylib/gyp/msvs_emulation.py
+++ b/pylib/gyp/msvs_emulation.py
@@ -614,10 +614,17 @@ class MsvsSettings(object):
     ld('Profile', map={'true': '/PROFILE'})
     ld('LargeAddressAware',
         map={'1': ':NO', '2': ''}, prefix='/LARGEADDRESSAWARE')
-    ld('ImageHasSafeExceptionHandlers', map={'true': '/SAFESEH'})
     # TODO(scottmg): This should sort of be somewhere else (not really a flag).
     ld('AdditionalDependencies', prefix='')
 
+    if self.GetArch(config) == 'x86':
+      safeseh_default = 'true'
+    else:
+      safeseh_default = None
+    ld('ImageHasSafeExceptionHandlers',
+        map={'false': ':NO', 'true': ''}, prefix='/SAFESEH',
+        default=safeseh_default)
+
     # If the base address is not specifically controlled, DYNAMICBASE should
     # be on by default.
     base_flags = filter(lambda x: 'DYNAMICBASE' in x or x == '/FIXED',