Mk/*: unconditionally use .MAKE.UID and .MAKE.GID

Since FreeBSD 12 has been EOLed, the built-in make(1) variables
.MAKE.UID and .MAKE.GID are always available.

PR:		276259
Approved by:	arrowd

Mk/Uses/uidfix.mk

@@ -8,9 +8,7 @@
 
 .if !defined(_INCLUDE_USES_UIDFIX_MK)
 _INCLUDE_USES_UIDFIX_MK=	yes
-.  if !defined(GID)
-GID!=	id -g
-.  endif
+GID?=	${.MAKE.GID}
 .  if ${UID} != 0
 MAKE_ENV+=	BINOWN=${UID} SHAREOWN=${UID} CONFOWN=${UID} LIBOWN=${UID}
 MAKE_ENV+=	BINGRP=${GID} SHAREGRP=${GID} CONFGRP=${GID} LIBGRP=${GID}

Mk/bsd.port.mk

@@ -1448,13 +1448,7 @@ USES+=mysql:${USE_MYSQL}
 .include "${PORTSDIR}/Mk/bsd.wx.mk"
 .    endif
 
-.    if !defined(UID)
-.      if defined(.MAKE.UID)
-UID=	${.MAKE.UID}
-.      else
-UID!=	${ID} -u
-.      endif
-.    endif
+UID?=	${.MAKE.UID}
 
 DESTDIRNAME?=	DESTDIR
 

Mk/bsd.port.subdir.mk

@@ -137,9 +137,7 @@ _JAVA_PORTS_INSTALLED!=		${MAKE} -V _JAVA_PORTS_INSTALLED USE_JAVA=1 -f ${PORTSD
 .  endif
 _EXPORTED_VARS+=	_JAVA_PORTS_INSTALLED
 
-.  if !defined(UID)
-UID!=	${ID} -u
-.  endif
+UID?=	${.MAKE.UID}
 _EXPORTED_VARS+=	UID
 
 .endif