kernel32: Implement IsThreadAFiber function.

dlls/kernel32/fiber.c

@@ -304,3 +304,11 @@ BOOL WINAPI FlsSetValue( DWORD index, PVOID data )
     NtCurrentTeb()->FlsSlots[index] = data;
     return TRUE;
 }
+
+/***********************************************************************
+ *           IsThreadAFiber   (KERNEL32.@)
+ */
+BOOL WINAPI IsThreadAFiber(void)
+{
+    return NtCurrentTeb()->Tib.u.FiberData != NULL;
+}

dlls/kernel32/kernel32.spec

@@ -749,6 +749,7 @@
 @ stdcall IsProcessorFeaturePresent(long)
 @ stub -i386 IsSLCallback
 @ stdcall IsSystemResumeAutomatic()
+@ stdcall IsThreadAFiber()
 @ stdcall IsValidCodePage(long)
 @ stdcall IsValidLanguageGroup(long long)
 @ stdcall IsValidLocale(long long)

dlls/kernel32/tests/fiber.c

@@ -146,7 +146,7 @@ static void test_FiberHandling(void)
 
     if (!pIsThreadAFiber)
     {
-        skip( "IsThreadAFiber not present\n" );
+        win_skip( "IsThreadAFiber not present\n" );
         return;
     }