CMAKE_BUILD_PARALLEL_LEVEL
Specifies the maximum number of concurrent processes to use when building using the cmake --build command line Build Tool Mode.
If this variable is defined empty the native build tool’s default number is used.
© 2000–2019 Kitware, Inc. and Contributors
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.12/envvar/CMAKE_BUILD_PARALLEL_LEVEL.html