Optimize github runners:

- Remove clang 3.5
- Print used cores
- Remove debug symbols

.github/workflows/ci.yml

@@ -145,15 +145,6 @@ jobs:
           #------------------
           # Linux, clang
           #------------------
-          # Linux, clang-3.5
-          - toolset: clang
-            compiler: clang++-3.5
-            cxxstd: "03,11"
-            cxxflags: -pipe
-            os: ubuntu-latest
-            container: ubuntu:16.04
-            install:
-              - clang-3.5
           # Linux, clang-3.6
           - toolset: clang
             compiler: clang++-3.6
@@ -503,6 +494,7 @@ jobs:
             echo REF: $REF
             BOOST_BRANCH=develop && [ "$REF" = "master" ] && BOOST_BRANCH=master || true
             echo BOOST_BRANCH: $BOOST_BRANCH
+            echo BUILD_JOBS: $BUILD_JOBS
             BUILD_JOBS=$((nproc || sysctl -n hw.ncpu) 2> /dev/null)
             echo "BUILD_JOBS=$BUILD_JOBS" >> $GITHUB_ENV
             echo "CMAKE_BUILD_PARALLEL_LEVEL=$BUILD_JOBS" >> $GITHUB_ENV
@@ -573,7 +565,7 @@ jobs:
         if: matrix.cmake_tests == ''
         run: |
             cd boost-root
-            B2_ARGS=("-j" "$BUILD_JOBS" "toolset=${{matrix.toolset}}" "cxxstd=${{matrix.cxxstd}}")
+            B2_ARGS=("-j" "$BUILD_JOBS" "toolset=${{matrix.toolset}}" "cxxstd=${{matrix.cxxstd}}" "debug-symbols=off")
             if [ -n "${{matrix.build_variant}}" ]
             then
                 B2_ARGS+=("variant=${{matrix.build_variant}}")
@@ -646,6 +638,7 @@ jobs:
             set BOOST_BRANCH=develop
             for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
             echo BOOST_BRANCH: %BOOST_BRANCH%
+            echo NUMBER_OF_PROCESSORS: %NUMBER_OF_PROCESSORS%
             mkdir snapshot
             cd snapshot
             echo Downloading library snapshot: https://github.com/%GITHUB_REPOSITORY%/archive/%GITHUB_SHA%.zip
@@ -673,5 +666,5 @@ jobs:
         shell: cmd
         run: |
             cd boost-root
-            b2 -j %NUMBER_OF_PROCESSORS% libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release embed-manifest-via=linker
+            b2 -j %NUMBER_OF_PROCESSORS% libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release embed-manifest-via=linker debug-symbols=off