[SV 61226] Revert changes to detect missing included files

[SV 61226] Revert changes to detect missing included files

The fix for SV 60595 introduced a backward-incompatibility: rules that
purported to rebuild included files, but didn't actually do so, were
treated as errors whereas before they were ignored.  This breaks a
common idiom in makefiles where an empty recipe is created for an
included makefile so make doesn't complain if it doesn't exist.

Unfortunately this means make cannot diagnose some types of errors.

Extra tests supplied by Dmitry Goncharov <dgoncharov@users.sf.net>.

* doc/make.texi (Including Other Makefiles): Clarify this behavior.
* src/main.c (main): Don't run the new check-for-errors behavior.
* tests/scripts/features/reinvoke: Reset tests of the "old" behavior
and add new tests for this situation.