Add wchar_t overloads to utf.h for C++ on Windows with non-MSVC compilers; I did not realize that was also a thing I needed to worry about!

Update #287

common/utf.h

@@ -28,12 +28,52 @@ extern size_t uiprivUTF16UTF8Count(const uint16_t *s, size_t nElem);
 #ifdef __cplusplus
 }
 
-// Provide overloads on Windows for using these functions with wchar_t and WCHAR when wchar_t is a keyword in C++ mode (the default).
+// TODO sync this back to upstream (need copyright clearance first)
-// Otherwise, you'd need to cast to pass a wchar_t pointer, WCHAR pointer, or equivalent to these functions.
+
-// We use __wchar_t to be independent of the setting; see https://blogs.msdn.microsoft.com/oldnewthing/20161201-00/?p=94836 (ironically posted one day after I initially wrote this code!).
+// On Windows, wchar_t is equivalent to uint16_t, but C++ requires
-// TODO check this on MinGW-w64
+// wchar_t to be a completely distinct type. These overloads allow
+// passing wchar_t pointers directly into these functions from C++
+// on Windows. Otherwise, you'd need to cast to pass a wchar_t
+// pointer, WCHAR pointer, or equivalent to these functions.
+// 
+// This does not apply to MSVC because the situation there is
+// slightly more complicated; see below.
+#if defined(_WIN32) && !defined(_MSC_VER)
+
+inline size_t uiprivUTF16EncodeRune(uint32_t rune, wchar_t *encoded)
+{
+	return uiprivUTF16EncodeRune(rune, reinterpret_cast<uint16_t *>(encoded));
+}
+
+inline const wchar_t *uiprivUTF16DecodeRune(const wchar_t *s, size_t nElem, uint32_t *rune)
+{
+	const uint16_t *ret;
+
+	ret = uiprivUTF16DecodeRune(reinterpret_cast<const uint16_t *>(s), nElem, rune);
+	return reinterpret_cast<const wchar_t *>(ret);
+}
+
+inline size_t uiprivUTF16RuneCount(const wchar_t *s, size_t nElem)
+{
+	return uiprivUTF16RuneCount(reinterpret_cast<const uint16_t *>(s), nElem);
+}
+
+inline size_t uiprivUTF16UTF8Count(const wchar_t *s, size_t nElem)
+{
+	return uiprivUTF16UTF8Count(reinterpret_cast<const uint16_t *>(s), nElem);
+}
+
+#endif
+
+// This is the same as the above, except that with MSVC, whether
+// wchar_t is a keyword or not is controlled by a compiler option!
+// (At least with gcc, this is not the case; thanks redi in
+// irc.freenode.net/#gcc.) We use __wchar_t to be independent of
+// the option; see https://blogs.msdn.microsoft.com/oldnewthing/20161201-00/?p=94836
+// (ironically posted one day after I initially wrote this code!).
+// TODO should defined(_WIN32) be used too?
 // TODO check this under /Wall
-// TODO C-style casts enough? or will that fail in /Wall?
+// TODO are C-style casts enough? or will that fail in /Wall?
 // TODO same for UniChar/unichar on Mac? if both are unsigned then we have nothing to worry about
 #if defined(_MSC_VER)