Force MSVC to use exception handling

As of 8.18.0, libvips C++ wrapper retrieves error messages at
exception construction time rather than lazily when accessed.

On Windows this led to error messages being referenced rather
than copied, leading to access beyond their lifetime and possible
corruption.

src/binding.gyp

@@ -21,6 +21,7 @@
         'defines': [
           '_VIPS_PUBLIC=__declspec(dllexport)',
           '_ALLOW_KEYWORD_MACROS',
+          '_HAS_EXCEPTIONS=1',
           'G_DISABLE_ASSERT',
           'G_DISABLE_CAST_CHECKS',
           'G_DISABLE_CHECKS'
@@ -148,7 +149,8 @@
           ['OS == "win"', {
             'defines': [
               '_ALLOW_KEYWORD_MACROS',
-              '_FILE_OFFSET_BITS=64'
+              '_FILE_OFFSET_BITS=64',
+              '_HAS_EXCEPTIONS=1'
             ],
             'link_settings': {
               'libraries': [