[Ada] Remove unused define

[Pierre-Marie de Rodat]

__MINWGW32__ is typo and was not working, but anyway the MSG_WAITALL
is defined on Windows.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* s-oscons-tmplt.c (MSG_WAITALL): Remove wrong #ifdef
	__MINWGW32__.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.diff
Type: text/x-diff
Size: 556 bytes
Desc: not available
URL: <https://gcc.gnu.org/pipermail/gcc-patches/attachments/20210707/ea80fea3/attachment.bin>