[PATCH] _cxa_thread_atexit fixes for Cygwin/MinGW-w64

[Yaakov Selkowitz <yselkowi at redhat dot com>]

The attached patch implements premature DLL unloading prevention in 
__cxa_thread_atexit for Cygwin and MinGW-w64 targets.  The mingw.org 
target is welcome to do the same in their os_defines.h, but this code 
does require Windows XP/2003, and they have historically catered to 
older platforms.

MinGW cannot practically implement __cxa_thread_atexit_impl because it 
has no control over the contents of its libc (msvcrt), and implementing 
this in the (static) mingw32 support library would be of little benefit 
because it would still end up statically linked into libstdc++.  Also, 
the GPL-with-exceptions libstdc++ implementation cannot be copied as a 
basis of our own __cxa_thread_atexit_impl due to licensing conflicts 
with both Cygwin (copyright assignment) and MinGW (public domain).

The testsuite shows no regressions with this patch.

--
Yaakov Selkowitz
Associate Software Engineer, ARM
Red Hat, Inc.

Attachment: 0006-libsupc-atexit_thread-cygming.patch
Description: Text document