make distclean blows away include/libint2, resulting in build failures

[mbanck]

Just running make distclean on a fresh checkout results in include/libint2 being deleted and then a subsequent build failing with an obscure error message about "C++11 support is required" when in fact it can not find ./include/libint2/util/cxxstd.h anymore. I believe it is general development consensus that make distclean should not remove any files required to build the project again from scratch and/or any files from git which can not be regenerated by the build system.

$ LANG=C make distclean
for dir in src tests/eri tests/unit tests/hartree-fock doc tests/eri tests/unit tests/hartree-fock; \
  do \
    (cd ${dir} && make "DODEPEND=no" distclean) || exit 1; \
  done
make[1]: Entering directory '/home/mba/hacking/git/libint/src'
[...]
make[1]: Leaving directory '/home/mba/hacking/git/libint/tests/hartree-fock'
rm -rf autom4te.cache config.status config.log conf*.file conf*.dir *.dSYM depcheck* libtool \
Makedirlist libint2.pc include/libint2
test -f libint2.pc.in || rm -rf include/libint2
$ LANG=C git status | head
On branch master
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
  (use "git add/rm <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	deleted:    include/libint2/atom.h
	deleted:    include/libint2/basis.h.in
	deleted:    include/libint2/boys.h
$ ./autogen.sh
$ ./configure
checking build system type... x86_64-pc-linux-gnu
[...]
checking CXX for array... yes
configure: error: C++11 support is required to compile the Libint compiler. Obtain a recent C++ compiler that supports C++11, or consider using a pregenerated library
$ grep conftest.*fatal.error config.log | grep -v ac_nonexistent.h
conftest.cpp:55:18: fatal error: ./include/libint2/util/cxxstd.h: No such file or directory
conftest.cpp:55:19: fatal error: ./include/libint2/util/cxxstd.h: No such file or directory

[e-kwsm]

The directory is removed by

libint/Makefile

Lines 90 to 92 in 5bb5fcf

	-rm -rf autom4te.cache config.status config.log conf*.file conf*.dir *.dSYM depcheck* libtool \
	Makedirlist libint2.pc include/libint2
	test -f libint2.pc.in || rm -rf include/libint2

.

[evaleev]

This will be addressed by #205