environ: fix link error on 64-bit Cygwin

[Ken Brown]

On 1/31/2018 9:40 AM, Corinna Vinschen wrote:
> On Jan 31 07:52, Eric Blake wrote:
>> Forwarding from the gnulib list; is this something we should fix in
>> cygwin proper?
> 
> Why does anybody remove the -Wl,--disable-auto-import flag?  What for?
> The idea was to never use this flag on Cygwin and to get rid of the
> dllimport/dllexport nonsense...
> 
>> On 01/31/2018 04:42 AM, Bruno Haible wrote:
>>> On 64-bit Cygwin, a libunistring build fails like this:
>>> [...]
>>> libtool: link: x86_64-pc-cygwin-gcc -g -O2 -Wl,--disable-auto-import -o .libs/test-environ.exe test-environ.o  -L/usr/local/cygwin64/lib libtests.a ../lib/.libs/libunistring.dll.a -liconv libtests.a -L/usr/local/cygwin64/lib
>>> test-environ.o:test-environ.c:(.rdata$.refptr.environ[.refptr.environ]+0x0): undefined reference to `environ'
>>> collect2: error: ld returned 1 exit status
>>>
>>> This fixes it.
>>> [...]
>>> +_GL_EXTERN_C __declspec(dllimport) char **environ;
> 
> But, other than that, an equivalent newlib patch would be ok.

Before patching newlib, please note that Bruno's patch doesn't work on 
32-bit Cygwin.  Projects (like emacs and clisp) that use gnulib's unistd 
module with that patch will get link errors like this:

   undefined reference to `_imp__environ'

I have no idea why this error occurs only on 32-bit.

I've made Bruno aware of the problem, and I'm waiting to see what he 
comes up with.

Ken

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