move SK_MMAP_SUPPORT into SkPreConfig, so we can know about its availability

trunk/gyp/core.gyp

 # Core Skia library code.
 {
   'targets': [
     {
       'target_name': 'core',
       'product_name': 'skia_core',
       'type': 'static_library',
       'standalone_static_library': 1,
       'msvs_guid': 'B7760B5E-BFA8-486B-ACFD-49E3A6DE8E76',
 
@@ skipping 56 matching lines @@
               '$(SDKROOT)/System/Library/Frameworks/OpenGLES.framework',
               '$(SDKROOT)/System/Library/Frameworks/ImageIO.framework',
               '$(SDKROOT)/System/Library/Frameworks/MobileCoreServices.framework',
             ],
           },
         }],
         [ 'skia_os == "win"', {
           'include_dirs': [
             'config/win',
           ],
-          'sources!': [
-            '../include/core/SkMMapStream.h',
-            '../src/core/SkMMapStream.cpp',
-          ],
         }],
         [ 'skia_os in ("android", "nacl")', {
           'dependencies': [
             'freetype.gyp:freetype',
           ],
         }],
         [ 'skia_os == "android" and skia_arch_type == "arm" and armv7 == 1', {
           # The code in SkUtilsArm.cpp can be used on an ARM-based Linux system, not only Android.
           'sources': [
             '../src/core/SkUtilsArm.cpp',
@@ skipping 40 matching lines @@
       ],
     },
   ],
 }
 
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