Multi-word MAKEFLAGS doesn't work properly

We ran into this issue when upgrading Kati on AOSP, but I've solved this on our side separately by clearing MAKEFLAGS, since we don't want the MAKEFLAGS override behavior and the variables are already available in the environment.

Simple shell testcase to drop into testcase/cmdline_var_spaces.sh:

``` shell
set -e

mk="$@"

cat < Makefile
ifdef SUBMAKE
all:
+@\$(SUBMAKE) SUBMAKE=
else
CLVAR := FAIL
CLVAR_RESULT := FAIL
ifeq (\$(CLVAR),multi word)
CLVAR_RESULT := PASS
endif
all:
@echo \$(CLVAR_RESULT) \$(CLVAR) \$(origin CLVAR)
endif
EOF

make SUBMAKE="${mk}" CLVAR='multi word' 2> /dev/null
```

Which prints out:

```
(make) PASS multi word command line
(ckati) FAIL multi command line
```

If you print out $(MAKEFLAGS), the makeflags is written as:

```
CLVAR=multi\ word SUBMAKE=../../ckati\ SHELL=/bin/bash
```

So kati's MAKEFLAGS parsing needs to handle the escaped spaces (I'm not sure if anything else can be escaped)