build: fix issues in the generated tarball

Reported by Andre da Costa Barros.
https://savannah.gnu.org/patch/?9716

* examples/calc++/local.mk: We no longer generate position.hh and
stack.hh.  Leaving them here triggers their concurrent generation,
which fails.
(%C%_calc___CPPFLAGS): Fix the extracted headers in the source tree.
* examples/mfcalc/local.mk (%C%_mfcalc_CPPFLAGS): Ditto.

examples/calc++/local.mk

@@ -57,9 +57,7 @@ extracted += $(calcxx_extracted)
 calcxx_sources_generated =                      \
   %D%/parser.cc                                 \
   %D%/parser.hh                                 \
-  %D%/location.hh                               \
-  %D%/position.hh                               \
-  %D%/stack.hh
+  %D%/location.hh
 calcxx_sources =                                \
   $(calcxx_sources_extracted)                   \
   $(calcxx_sources_generated)
@@ -69,7 +67,7 @@ if  ENABLE_CXX
   check_PROGRAMS += %D%/calc++
   nodist_%C%_calc___SOURCES = $(calcxx_sources)
   # Don't use gnulib's system headers.
-  %C%_calc___CPPFLAGS = -I$(top_builddir)/%D%
+  %C%_calc___CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
   %C%_calc___CXXFLAGS = $(AM_CXXFLAGS) $(FLEX_SCANNER_CXXFLAGS)
   TESTS += %D%/calc++.test
 endif  ENABLE_CXX

examples/mfcalc/local.mk

@@ -29,7 +29,7 @@ extracted += $(mfcalc_extracted)
 check_PROGRAMS += %D%/mfcalc
 nodist_%C%_mfcalc_SOURCES = $(mfcalc_sources)
 # Don't use gnulib's system headers.
-%C%_mfcalc_CPPFLAGS = -I$(top_builddir)/%D%
+%C%_mfcalc_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
 %C%_mfcalc_LDADD = -lm
 
 dist_TESTS += %D%/mfcalc.test