<http://webkit.org/b/106742>

Fixes the following build failures:

    Undefined symbols for architecture i386:
      "__ZTVN7WebCore25PlatformSpeechSynthesizerE", referenced from:
          __ZN7WebCore25PlatformSpeechSynthesizerC2EPNS_31PlatformSpeechSynthesizerClientE in PlatformSpeechSynthesizer.o
      NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
      "__ZN7WebCore25PlatformSpeechSynthesizer19initializeVoiceListEv", referenced from:
          __ZN7WebCore25PlatformSpeechSynthesizerC2EPNS_31PlatformSpeechSynthesizerClientE in PlatformSpeechSynthesizer.o
    ld: symbol(s) not found for architecture i386

Source/JavaScriptCore:

* Configurations/FeatureDefines.xcconfig:
- Fix definition of ENABLE_ENCRYPTED_MEDIA_V2_macosx to match
  other FeatureDefines.xcconfig files.
- Only set ENABLE_SPEECH_SYNTHESIS for the macosx platform.

Source/WebCore:

* Configurations/FeatureDefines.xcconfig:
- Only set ENABLE_SPEECH_SYNTHESIS for the macosx platform.

Source/WebKit/mac:

* Configurations/FeatureDefines.xcconfig:
- Only set ENABLE_SPEECH_SYNTHESIS for the macosx platform.

Source/WebKit2:

* Configurations/FeatureDefines.xcconfig:
- Only set ENABLE_SPEECH_SYNTHESIS for the macosx platform.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144764 268f45cc-cd09-0410-ab3c-d52691b4dbfc