build: configure parallel jobs

lua-Harness and tarantool testsuites uses a prove(1) for running tests.
prove(1) allows to run tests in parallel with option "--jobs" [1].

In CMake it is not possible to get a number of parallel jobs in CMake
passed by user with option "-j", but it allows to pass a number of
parallel jobs with environment variable CMAKE_BUILD_PARALLEL_LEVEL [2]
on configuration phase. We use a value set by that environment variable
and set it to a number of CPU threads when it was not specified by user.
Number of CPU threads detected using builtin CMake function [3].

NOTE: CMAKE_BUILD_PARALLEL_LEVEL has been added in a version 3.12.

1. https://perldoc.perl.org/prove
2. https://cmake.org/cmake/help/latest/envvar/CMAKE_BUILD_PARALLEL_LEVEL.html
3. https://cmake.org/cmake/help/latest/module/ProcessorCount.html

test/CMakeLists.txt

@@ -43,6 +43,19 @@ endif()
 set(LUAJIT_TEST_COMMAND "${LUAJIT_TEST_BINARY} -e dofile[[${LUAJIT_TEST_INIT}]]")
 separate_arguments(LUAJIT_TEST_COMMAND)
 
+set(CMAKE_BUILD_PARALLEL_LEVEL $ENV{CMAKE_BUILD_PARALLEL_LEVEL})
+if(NOT CMAKE_BUILD_PARALLEL_LEVEL)
+  include(ProcessorCount)
+  ProcessorCount(N)
+  # Function ProcessorCount() is guaranteed to return a positive integer (>=1)
+  # if it succeeds. It returns 0 if there's a problem determining the processor
+  # count.
+  if(NOT N EQUAL 0)
+    set(CMAKE_BUILD_PARALLEL_LEVEL ${N})
+  endif()
+endif()
+message(STATUS "Using CMAKE_BUILD_PARALLEL_LEVEL: ${CMAKE_BUILD_PARALLEL_LEVEL}")
+
 add_subdirectory(LuaJIT-tests)
 add_subdirectory(PUC-Rio-Lua-5.1-tests)
 add_subdirectory(lua-Harness-tests)

test/lua-Harness-tests/CMakeLists.txt

@@ -28,6 +28,7 @@ add_custom_command(TARGET lua-Harness-tests
     LUA_PATH="${LUA_PATH}\;"
     ${PROVE} ${CMAKE_CURRENT_SOURCE_DIR}
       --exec '${LUAJIT_TEST_COMMAND} -l profile_luajit21'
+      --jobs ${CMAKE_BUILD_PARALLEL_LEVEL}
       ${LUA_TEST_FLAGS}
   WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
 )

test/tarantool-tests/CMakeLists.txt

@@ -136,6 +136,7 @@ add_custom_command(TARGET tarantool-tests
     ${PROVE} ${CMAKE_CURRENT_SOURCE_DIR}
       --exec 'env ${LUA_TEST_ENV_MORE} ${LUAJIT_TEST_COMMAND}'
       --ext ${LUA_TEST_SUFFIX}
+      --jobs ${CMAKE_BUILD_PARALLEL_LEVEL}
       ${LUA_TEST_FLAGS}
   WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
 )