Escaped percent char is mishandled in patsubst arguments

[asmundak]

According to https://www.gnu.org/software/make/manual/make.html#Text-Functions,
"‘%’ characters in patsubst function invocations can be quoted with preceding backslashes (‘\’). "
Kati does not do that:

$ cat /tmp/a.mk
$(error $(patsubst %,\%/%,a b c))
$ make -f /tmp/a.mk 
/tmp/a.mk:1: *** %/a %/b %/c.  Stop.
$ ckati -f /tmp/a.mk 
/tmp/a.mk:1: *** \a/% \b/% \c/%.

[danw]

I had noticed this as well very early on in switching to Kati, though decided I had better things to do since we couldn't find a single case of a user actually using this in the Android trees. Considering how often patsubst was used I was also worried about the overhead of extra logic, though I suspect that's much less of a problem these days (as more work has been pushed out of Make).