Work around a compiler bug in MacOS AppleClang 11 (#6103)

* Workaround a compiler bug in MacOS AppleClang

* [CI] Run C++ test with MacOS Catalina + AppleClang 11.0.3

* [CI] Migrate cmake_test on MacOS from Travis CI to GitHub Actions

* Install OpenMP runtime

* [CI] Use CMake to locate lz4 lib

tests/travis/run_test.sh

@@ -17,6 +17,12 @@ if [ ${TASK} == "python_sdist_test" ]; then
 fi
 
 if [ ${TASK} == "python_test" ]; then
+    if grep -n -R '<<<.*>>>\(.*\)' src include | grep --invert "NOLINT"; then
+        echo 'Do not use raw CUDA execution configuration syntax with <<<blocks, threads>>>.' \
+             'try `dh::LaunchKernel`'
+        exit -1
+    fi
+
     set -e
     # Build/test
     rm -rf build
@@ -69,26 +75,6 @@ if [ ${TASK} == "java_test" ]; then
     mvn -q test
 fi
 
-if [ ${TASK} == "cmake_test" ]; then
-    set -e
-
-    if grep -n -R '<<<.*>>>\(.*\)' src include | grep --invert "NOLINT"; then
-        echo 'Do not use raw CUDA execution configuration syntax with <<<blocks, threads>>>.' \
-             'try `dh::LaunchKernel`'
-        exit -1
-    fi
-
-    # Build/test
-    rm -rf build
-    mkdir build && cd build
-    PLUGINS="-DPLUGIN_LZ4=ON -DPLUGIN_DENSE_PARSER=ON"
-    cmake .. -DCMAKE_VERBOSE_MAKEFILE=ON -DGOOGLE_TEST=ON -DUSE_OPENMP=ON -DUSE_DMLC_GTEST=ON ${PLUGINS}
-    make -j$(nproc)
-    ./testxgboost
-    cd ..
-    rm -rf build
-fi
-
 if [ ${TASK} == "s390x_test" ]; then
     set -e
 

tests/travis/setup.sh

@@ -16,10 +16,6 @@ if [ ${TASK} == "python_test" ] || [ ${TASK} == "python_sdist_test" ]; then
     conda create -n python3 python=3.7
 fi
 
-if [ ${TASK} == "cmake_test" ] && [ ${TRAVIS_OS_NAME} == "osx" ]; then
-    sudo softwareupdate -i "Command Line Tools (macOS High Sierra version 10.13) for Xcode-9.3"
-fi
-
 if [ ${TASK} == "s390x_test" ] && [ ${TRAVIS_CPU_ARCH} == "s390x" ]; then
     sudo snap install cmake --channel=3.17/beta --classic
     export PATH=/snap/bin:${PATH}