Fix for issue #19086 RCTHasFontHandlerSet(); This function definition…

Summary:
… is not a protoype #19086

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Fixes #19086

Related to react-native-navigation issue #3019

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Created a fresh react native >= 0.55.2 project and only install React Native Navigation. The error "This function declaration is not a prototype" message occurs.

Downgrading to React Native 0.54.4 builds fine.

![screen shot 2018-05-01 at 3 17 51 pm](https://user-images.githubusercontent.com/5680239/39491718-ddfdd6a0-4d52-11e8-937f-7ed9702a2e30.png)

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No documentation change

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[iOS] [BUGFIX] [react-native-navigation] - For compatibility with react-native-navigation >= 2.0.2237 https://github.com/facebook/react-native/issues/19086
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    CATEGORY
  [----------]      TYPE
  [ CLI      ] [-------------]    LOCATION
  [ DOCS     ] [ BREAKING    ] [-------------]
  [ GENERAL  ] [ BUGFIX      ] [ {Component} ]
  [ INTERNAL ] [ ENHANCEMENT ] [ {Filename}  ]
  [ IOS      ] [ FEATURE     ] [ {Directory} ]   |-----------|
  [ ANDROID  ] [ MINOR       ] [ {Framework} ] - | {Message} |
  [----------] [-------------] [-------------]   |-----------|

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
Closes https://github.com/facebook/react-native/pull/19089

Differential Revision: D7841198

Pulled By: shergin

fbshipit-source-id: 31638274055c3f143342d2d6dde6d4af7a2ac304

React/Views/RCTFont.h

@@ -18,7 +18,7 @@ typedef UIFont *(^RCTFontHandler)(CGFloat fontSize, NSString *fontWeightDescript
  * "semibold", "extrabold", "bold", "heavy", or "black".
  */
 RCT_EXTERN void RCTSetDefaultFontHandler(RCTFontHandler handler);
-RCT_EXTERN BOOL RCTHasFontHandlerSet();
+RCT_EXTERN BOOL RCTHasFontHandlerSet(void);
 
 @interface RCTFont : NSObject