GHA: Set N parallelism dynamically

To adapt automatically to the number of available CPU cores.

.github/workflows/main.yml

@@ -78,7 +78,7 @@ jobs:
       OS_NAME: ${{ startsWith(matrix.os, 'ubuntu') && 'linux' || (startsWith(matrix.os, 'macos') && 'osx' || (startsWith(matrix.os, 'windows') && 'windows' || '')) }}
       MODEL: ${{ matrix.model || '64' }}
       HOST_DMD: ${{ matrix.host_dmd }}
-      N: ${{ startsWith(matrix.os, 'macos') && '3' || '4' }}
+      # N is set dynamically below
       FULL_BUILD: true
       # for coverage:
       DMD_TEST_COVERAGE: ${{ matrix.coverage && '1' || '0' }}
@@ -92,6 +92,9 @@ jobs:
         with:
           fetch-depth: 50
 
+      - name: Set environment variable N (parallelism)
+        run: echo "N=$(${{ runner.os == 'macOS' && 'sysctl -n hw.logicalcpu' || 'nproc' }})" >> $GITHUB_ENV
+
       - name: 'Posix: Install prerequisites'
         if: runner.os != 'Windows'
         run: ${{ runner.os == 'macOS' && 'ci/cirrusci.sh' || 'sudo -E ci/cirrusci.sh' }}
@@ -195,7 +198,7 @@ jobs:
             export OS_NAME=freebsd
             export MODEL=64
             export HOST_DMD='${{ matrix.host_dmd }}'
-            export N=3
+            export N="$(nproc)"
             export FULL_BUILD=true
             export CI_DFLAGS="-version=TARGET_FREEBSD${freebsd_major}"
 

.github/workflows/runnable_cxx.yml

@@ -135,10 +135,12 @@ jobs:
     # Using a specific version for reproductibility.
     # Feel free to update when a new release has matured.
     runs-on: ${{ matrix.os }}
-    env:
-      N: ${{ startsWith(matrix.os, 'macos') && '3' || '4' }}
     steps:
 
+    - name: Set environment variable N (parallelism)
+      shell: bash
+      run: echo "N=$(${{ runner.os == 'macOS' && 'sysctl -n hw.logicalcpu' || 'nproc' }})" >> $GITHUB_ENV
+
     ########################################
     #    Setting up the host D compiler    #
     ########################################