Bugfix Makefile race condition betwen all and doc

When running make in parallel with -j or -j <n>: make -j all doc
then sometimes the doc target could start while the all target had
created all .erl files from .xrl and .yrl files, resulting in edoc
starting off on only half-ready files, promptly getting into trouble.
Workaround for bug in enif_make_int64
Prepare for 3.12.2