ARROW-6447: [C++] Allow rest of arrow_objlib to build in parallel while memory_pool.cc is waiting on jemalloc_ep

[wesm]

Using OBJECT_DEPENDS like this seems to only work with the Ninja build generator with CMake 3.12.x, which is probably a bug. With Makefiles we fall back to the old strategy of blocking on the completion of jemalloc_ep.

[wesm]

Ugh. Apparently this doesn't work with the Makefiles generator. I'm adding a case to fall back to the old dependency strategy when we aren't using Ninja

[codecov-io]

Codecov Report

Merging #5281 into master will increase coverage by 1.55%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5281      +/-   ##
==========================================
+ Coverage   87.67%   89.22%   +1.55%     
==========================================
  Files        1033      750     -283     
  Lines      149292   108330   -40962     
  Branches     1437        0    -1437     
==========================================
- Hits       130885    96654   -34231     
+ Misses      18045    11676    -6369     
+ Partials      362        0     -362

Impacted Files	Coverage Δ
cpp/src/arrow/csv/column_builder.cc	95.54% <0%> (-1.49%)	⬇️
python/pyarrow/tests/test_pandas.py	95.21% <0%> (-0.06%)	⬇️
python/pyarrow/tests/test_parquet.py	96.55% <0%> (ø)	⬆️
js/src/util/fn.ts
go/arrow/memory/memory_avx2_amd64.go
rust/datafusion/src/execution/filter.rs
rust/arrow/src/csv/writer.rs
rust/datafusion/src/bin/main.rs
go/arrow/ipc/file_reader.go
js/src/builder/index.ts
... and 276 more

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[wesm]

+1. I reported the issue with Makefiles to CMake

https://gitlab.kitware.com/cmake/cmake/issues/19677