Add possibility to split test suit build targets and improved CI configuration

- Introduce CMake option `EIGEN_SPLIT_TESTSUITE` that allows to divide the single test build target into several subtargets
- Add CI pipeline for merge request that can be run by GitLab's shared runners
- Add nightly CI pipeline

ci/build-tests.gitlab-ci.yml

@@ -0,0 +1,131 @@
+.build-tests-base:
+  stage: build
+  image: ubuntu:18.04
+  before_script:
+    - apt-get update -y
+    - apt-get install -y --no-install-recommends software-properties-common
+    - add-apt-repository -y  ppa:ubuntu-toolchain-r/test
+    - apt-get update
+    - apt-get install --no-install-recommends -y ${EIGEN_CI_CXX_COMPILER} ${EIGEN_CI_CC_COMPILER} cmake ninja-build
+  script:
+    - mkdir -p ${BUILDDIR} && cd ${BUILDDIR}
+    - echo "CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_SPLIT_TESTSUITE=${EIGEN_CI_TESTSUITE_SIZE} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} ${EIGEN_CI_ADDITIONAL_ARGS} .."
+    - CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_SPLIT_TESTSUITE=${EIGEN_CI_TESTSUITE_SIZE} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} ${EIGEN_CI_ADDITIONAL_ARGS}..
+    - echo "cmake --build . --target buildtestspart${EIGEN_CI_TESTSUITE_PART}"
+    - cmake --build . --target buildtestspart${EIGEN_CI_TESTSUITE_PART}
+  artifacts:
+    name: "$CI_JOB_NAME-$CI_COMMIT_REF_NAME"
+    paths:
+      - ${BUILDDIR}/
+    expire_in: 5 days
+
+# Base for all build jobs building the whole testsuite in one job. Note that
+# this cannot be run on GitLab's shared runners due to their timeout.
+.build-tests-single-base:
+  extends: .build-tests-base
+  script:
+    - mkdir -p ${BUILDDIR} && cd ${BUILDDIR}
+    - echo "CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} ${EIGEN_CI_CXX_FLAGS} ${EIGEN_CI_ADDITIONAL_ARGS}.."
+    - CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} ${EIGEN_CI_ADDITIONAL_ARGS}..
+    - echo "cmake --build . --target buildtests"
+    - cmake --build . --target buildtests
+  tags:
+    - eigen-runner
+    - x86
+    - linux
+  only:
+    - schedules
+
+# Base for all build jobs using a splitted testsuite such that the job can be
+# run on GitLab's own shared runners
+.build-tests-split-base:
+  extends: .build-tests-base
+  script:
+    - mkdir -p ${BUILDDIR} && cd ${BUILDDIR}
+    - echo "CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_SPLIT_TESTSUITE=${EIGEN_CI_TESTSUITE_SIZE} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} ${EIGEN_CI_CXX_FLAGS} -DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On .."
+    - CXX=${EIGEN_CI_CXX_COMPILER} CC=${EIGEN_CI_CC_COMPILER} cmake -G ${EIGEN_CI_CMAKE_GENEATOR} -DEIGEN_SPLIT_TESTSUITE=${EIGEN_CI_TESTSUITE_SIZE} -DEIGEN_TEST_CXX11=${EIGEN_TEST_CXX11} -DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On ..
+    - echo "cmake --build . --target buildtestspart${EIGEN_CI_TESTSUITE_PART}"
+    - cmake --build . --target buildtestspart${EIGEN_CI_TESTSUITE_PART}
+  only:
+    - merge_requests
+
+########################## Nightly running jobs ################################
+
+# GCC 4.8
+# This is the oldest GCC version we support
+build-tests-g++-4.8-cxx11-on:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-4.8"
+    EIGEN_CI_CC_COMPILER: "gcc-4.8"
+    EIGEN_TEST_CXX11: "on"
+
+build-tests-g++-4.8-cxx11-off:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-4.8"
+    EIGEN_CI_CC_COMPILER: "gcc-4.8"
+    EIGEN_TEST_CXX11: "off"
+
+# Clang 10
+build-tests-clang++-10-cxx11-on:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "clang++-10"
+    EIGEN_CI_CC_COMPILER: "clang-10"
+    EIGEN_TEST_CXX11: "on"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+
+build-tests-clang++-10-cxx11-off:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "clang++-10"
+    EIGEN_CI_CC_COMPILER: "clang-10"
+    EIGEN_TEST_CXX11: "off"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+
+# GCC 10
+build-tests-g++-10-cxx11-off:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-10"
+    EIGEN_CI_CC_COMPILER: "gcc-10"
+    EIGEN_TEST_CXX11: "off"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+
+build-tests-g++-10-cxx11-on:
+  extends: .build-tests-single-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-10"
+    EIGEN_CI_CC_COMPILER: "gcc-10"
+    EIGEN_TEST_CXX11: "on"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+
+########################### Merge request jobs #################################
+
+# GCC 10
+build-tests-g++-9-cxx11-on-mr:
+  only:
+    - merge_requests
+  extends: .build-tests-split-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-9"
+    EIGEN_CI_CC_COMPILER: "gcc-9"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+  parallel:
+    matrix:
+      - EIGEN_CI_TESTSUITE_PART: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
+        EIGEN_TEST_CXX11: "on"
+
+build-tests-g++-9-cxx11-off-mr:
+  only:
+    - merge_requests
+  extends: .build-tests-split-base
+  variables:
+    EIGEN_CI_CXX_COMPILER: "g++-9"
+    EIGEN_CI_CC_COMPILER: "gcc-9"
+    EIGEN_CI_ADDITIONAL_ARGS: "-DEIGEN_TEST_AVX=On -DEIGEN_TEST_AVX2=On"
+  parallel:
+    matrix:
+      - EIGEN_CI_TESTSUITE_PART: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
+        EIGEN_TEST_CXX11: "off"