crt: make iswblank always available in C++

Before this patch, wctype.h would make iswblank always available on C++,
but ctype.h and wchar.h would not. Since they share the same definition guard
macro, one could end up not getting iswblank in C++ when including
wctype.h after ctype.h / wchar.h .

This fixes this inconsistency by making it always available when
including those headers as well.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Signed-off-by: Liu Hao <lh_mouse@126.com>

mingw-w64-headers/crt/ctype.h

diff --git a/mingw-w64-headers/crt/ctype.h b/mingw-w64-headers/crt/ctype.h
index d6a1a54..bcac1c2 100644
--- a/mingw-w64-headers/crt/ctype.h
+++ b/mingw-w64-headers/crt/ctype.h
@@ -191,7 +191,7 @@
   int __cdecl is_wctype(wint_t _C,wctype_t _Type);
 #endif /* _CRT_USE_WINAPI_FAMILY_DESKTOP_APP */
 
-#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) || !defined (NO_OLDNAMES)
+#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) || !defined (NO_OLDNAMES) || defined (__cplusplus)
 int __cdecl iswblank(wint_t _C);
 #endif
 #endif

mingw-w64-headers/crt/wchar.h

diff --git a/mingw-w64-headers/crt/wchar.h b/mingw-w64-headers/crt/wchar.h
index ddafe77..ab71877 100644
--- a/mingw-w64-headers/crt/wchar.h
+++ b/mingw-w64-headers/crt/wchar.h
@@ -281,7 +281,7 @@
   int __cdecl is_wctype(wint_t _C,wctype_t _Type);
 #endif /* _CRT_USE_WINAPI_FAMILY_DESKTOP_APP */
 
-#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) || !defined (NO_OLDNAMES)
+#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) || !defined (NO_OLDNAMES) || defined (__cplusplus)
   int __cdecl iswblank(wint_t _C);
 #endif