make(1): fix unbalanced Lst_Open/Lst_Close in SuffFindCmds

This bug had been there since the initial import of make, on 1993-03-21.
It just never broke the build because of the missing assertion.

https://mail-index.netbsd.org/tech-toolchain/2020/08/30/msg003847.html

The error message "cd: can't cd to include" that I got when I first
applied the fix was unrelated.  It was caused by an extra directory
"include" in src/tools/compat that didn't belong there.  With that
directory removed, running "./build.sh -j8 tools" succeeds as expected.

(rillig)