[PATCH][PR build/23568] Fix gdb-7.12.1 MinGW/MSYS build issue

[Eli Zaretskii]

> From: Pedro Alves <palves@redhat.com>
> Date: Tue, 28 Aug 2018 17:57:43 +0100
> 
> On 08/28/2018 01:01 PM, SiZiOUS wrote:
> > This little patch was made to allow the compilation under the MinGW/MSYS legacy environment (I don't know for the newer MinGW-w64/MSYS2 environment!).
> > If this patch is not applied, then the compilation of gdb-7.12.1 under MinGW/MSYS is impossible.
> 
> GDB 7.12 is old by now and not actively maintained.
> 
> Can you check whether this is necessary on the master branch?

AFAICS, we include winerror.h via serial.h, which includes winsock2.h,
which includes winerror.h.  Older MinGW included that via the chain
windows.h->windef.h->winnt.h.

SiZiOUS, what version of the MinGW runtime are you using?