Fix generated code for building on MSVC 2013

This updates the script to generate code that is buildable by Visual Studio
2013 by:

-Using a macro to define the compiler-specific way to do noinline for a
 function, and use it when needed.

-Avoid using empty arrays and structs as that is a C99 feature that will
 likely be never support on Visual Studio as it is now an optional feature
 of C11.

src/gen_dispatch.py

@@ -577,8 +577,11 @@ class Generator(object):
             self.outln('    };')
 
             self.outln('    static const uint16_t entrypoints[] = {')
-            for provider in providers:
+            if len(providers) > 1:
-                self.outln('        {0} /* "{1}" */,'.format(self.entrypoint_string_offset[provider.name], provider.name))
+                for provider in providers:
+                    self.outln('        {0} /* "{1}" */,'.format(self.entrypoint_string_offset[provider.name], provider.name))
+            else:
+                    self.outln('        0 /* None */,')
             self.outln('    };')
 
             self.outln('    return {0}_provider_resolver(entrypoint_strings + {1} /* "{2}" */,'.format(self.target,
@@ -698,8 +701,8 @@ class Generator(object):
         self.outln('')
 
         single_resolver_proto = '{0}_single_resolver(enum {0}_provider provider, uint16_t entrypoint_offset)'.format(self.target)
-        self.outln('static void *')
+        self.outln('EPOXY_NOINLINE static void *')
-        self.outln('{0} __attribute__((noinline));'.format(single_resolver_proto))
+        self.outln('{0};'.format(single_resolver_proto))
         self.outln('')
         self.outln('static void *')
         self.outln('{0}'.format(single_resolver_proto))
@@ -728,6 +731,11 @@ class Generator(object):
         self.outln('#include "dispatch_common.h"')
         self.outln('#include "epoxy/{0}.h"'.format(self.target))
         self.outln('')
+        self.outln('#ifdef __GNUC__')
+        self.outln('#define EPOXY_NOINLINE __attribute__((noinline))')
+        self.outln('#elif defined (_MSC_VER)')
+        self.outln('#define EPOXY_NOINLINE __declspec(noinline)')
+        self.outln('#endif')
 
         self.outln('struct dispatch_table {')
         for func in self.sorted_functions: