Actually, bump Gmake builds to Windows 7.

Vista ended support before XP did, and it doesn't seem to show up
on any usage lists (while XP still has 0.27% of all Windows systems...
which are 25.46% of systems on the internet)

https://gs.statcounter.com/os-market-share

src/build/Common.gmake

@@ -247,10 +247,10 @@ endif
 os      :=	$(shell echo $(os) | tr '[A-Z]' '[a-z]' | tr ' ' '_')
 
 ifdef win
- WINNT ?= 0x0600
- WINVER ?= 0x0600
- WIN32_IE ?= 0x0700
- NTDDI ?= 0x06000000
+ WINNT ?= 0x0601
+ WINVER ?= 0x0601
+ WIN32_IE ?= 0x0800
+ NTDDI ?= 0x06010000
 else
  CFLAGS +=	-DPREFER_POLL
  machine_uname	:=	$(shell if uname -m | egrep -v "(i[3456789]*|x)86" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; fi)