[ffigen] Support Char_U type kind (#202)

pkgs/ffigen/lib/src/header_parser/type_extractor/cxtypekindmap.dart

diff --git a/pkgs/ffigen/lib/src/header_parser/type_extractor/cxtypekindmap.dart b/pkgs/ffigen/lib/src/header_parser/type_extractor/cxtypekindmap.dart
index 0fe81aa..7c7a936 100644
--- a/pkgs/ffigen/lib/src/header_parser/type_extractor/cxtypekindmap.dart
+++ b/pkgs/ffigen/lib/src/header_parser/type_extractor/cxtypekindmap.dart
@@ -24,6 +24,7 @@
   clang.CXTypeKind.CXType_Float: SupportedNativeType.Float,
   clang.CXTypeKind.CXType_Double: SupportedNativeType.Double,
   clang.CXTypeKind.CXType_Char_S: SupportedNativeType.Int8,
+  clang.CXTypeKind.CXType_Char_U: SupportedNativeType.Uint8,
   clang.CXTypeKind.CXType_Enum: SupportedNativeType.Int32,
 };