Support VAR:=value

[rasa]

Support:

VAR:=value

It currently treats VAR as a target:

Target "VAR" should be declared PHONY

[robbat2]

This check trips on the Linux kernel's stock Makefile, saying silence should be declared PHONY.
As a workaround, adding space, so it's silence := fixes the problem, so it sounds like the parser has a bug.

ifeq ("$(origin V)", "command line")
  KBUILD_VERBOSE = $(V)
endif
ifndef KBUILD_VERBOSE
  KBUILD_VERBOSE = 0
endif
ifeq ($(KBUILD_VERBOSE),1)
  quiet =
  Q =
else
  quiet=quiet_
  Q = @
endif
ifeq ($(filter 3.%,$(MAKE_VERSION)),)
silence:=$(findstring s,$(firstword -$(MAKEFLAGS)))
else
silence:=$(findstring s,$(filter-out --%,$(MAKEFLAGS)))
endif
export quiet Q KBUILD_VERBOSE