GCC 4.7 warns about maybe uninitialized variable _RetVal in widl-generated code with PSEH3

Widl generates proxy functions such as IInternetSecurityManager_GetZoneMappings_Proxy found in the attached widl-retval.c.
The _RetVal variable is unconditionally initialized in both try and except block, but GCC complains it "may be uninitialized":
dll/win32/urlmon/urlmon_urlmon_p.c:7485:5: warning: '_RetVal' may be used uninitialized in this function [-Wmaybe-uninitialized]

This makes for ~1400 warnings.