-fshort-wchar option, wchar_t and Native<->Unicode conversion

In 
http://lxr.mozilla.org/seamonkey/source/xpcom/io/nsNativeCharsetUtils.cpp#623,

it's assumed that *wchar_t is the same as *PRUnichar when 
gWCharIsUnicode is true. I'm wondering if it's always the case.

At the momemnt, Linux build is made with '-fshort-wchar' option to gcc. 
With that option, wchar_t is short(2byte) and *wchar_t is the same as 
*PRUnichar as far as non-BMP char is concerned. Even in that case, I'm 
not sure *wchar_t is identical to *PRUnichar. It's to be note that 
*PRUnichar is NOT a string of UCS2 BUT a 'UTF-16 string'. I'm not sure 
what gcc does when '-fshort-wchar' is turned on. That is, I'm wondering 
whether '-fshort-wchar' makes *wchar_t 'UTF-16 string' as opposed to 
'UCS2 string'. If not, UnicodeToNative and NativeToUnicode are broken 
for non-BMP characters.

Even more serious is that *wchar_t is a string of PRUInt32's on 
Linux(glibc,gcc) if '-fshort_wchar' is not used. How about other 
compilers on other platforms? '-fshort_wchar' is only available in gcc, 
isn't it? [1]


How about the interaction between '-fshort-wchar' and 
'__STDC_ISO_10646__' (ISO C 99)? If the latter is defined, wchar_t is 
supposed to be UCS4. Does '-fshort-wchar' override it? If so, do we plan 
to use '-fshort-wchar' permanently?

A possible work-around for this problem is to use 'iconv' in place of mb 
rtowc and wcrtomb.

Jungshik


[1]I'm aware that on some platforms, wchar_t is locale-dependent and 
it's not even ISO 10646/Unicode, but let's just leave it aside for this 
discussion.