MSVC Builds: Support PACKED

Define PACKED for Visual Studio builds, so that we can try to reduce
our library size for Visual Studio builds.  Add a ENDPACKED macro
that is currently defined only for Visual Studio builds as packing is
done via __pragma(pack(push,n), that should be popped when done.

Signed-off-by: Emmanuele Bassi <ebassi@gnome.org>

src/dispatch_common.h

@@ -68,8 +68,13 @@
 
 #if defined(__GNUC__)
 #define PACKED __attribute__((__packed__))
+#define ENDPACKED
+#elif defined (_MSC_VER)
+#define PACKED __pragma(pack(push,1))
+#define ENDPACKED __pragma(pack(pop))
 #else
 #define PACKED
+#define ENDPACKED
 #endif
 
 /* On win32, we're going to need to keep a per-thread dispatch table,

src/gen_dispatch.py

@@ -628,6 +628,7 @@ class Generator(object):
         # Writes the enum declaration for the list of providers
         # supported by gl_provider_resolver()
 
+        self.outln('')
         self.outln('enum {0}_provider {{'.format(self.target))
 
         sorted_providers = sorted(self.provider_enum.keys())
@@ -640,6 +641,7 @@ class Generator(object):
             enum = self.provider_enum[human_name]
             self.outln('    {0},'.format(enum))
         self.outln('} PACKED;')
+        self.outln('ENDPACKED')
         self.outln('')
 
     def write_provider_enum_strings(self):