libjemalloc: Compile in empty jemalloc_stub.c for HAVE_JEMALLOC=100

Fix strange parallel build failures observed on vax and sun2, which
should be due to empty SRCS.

No functional changes as library

libjemalloc: Compile in empty jemalloc_stub.c for HAVE_JEMALLOC=100

Fix strange parallel build failures observed on vax and sun2, which
should be due to empty SRCS.

No functional changes as library itself.

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this is not needed (or wanted) for jemalloc 1.0, so make it empty.

- descend to build libjemalloc
- namespace protect all functions __je
- provide getters and setters for malloc_conf and malloc_message

bump warns

Add Makefiles if we want to build jemalloc standalone.