test: more rerunning autotools, C++ std:: portability. Trying to fix more of https://bugs.gnu.org/68119. * t/aclocal-deleted-header-aclocal-amflags.sh: $sleep before file modifications. * t/aclocal-deleted-header.sh: likewise. * t/aclocal-deps.sh: likewise. * t/subdir-add2-pr46.sh: likewise. * t/yacc-mix-c-cxx.sh: #include <cstdlib> before using std::..., following yacc-cxx and yacc-d-cxx tests.