GHA: Allow setting defines, variant, and linkage via matrix

.github/workflows/ci.yml

@@ -226,27 +226,28 @@ jobs:
 
       - name: Setup multiarch
         if: matrix.multiarch
+        run: ci/github/setup_bdde.sh
         env:
           BDDE_DISTRO: ${{matrix.distro}}
           BDDE_EDITION: ${{matrix.edition}}
           BDDE_ARCH: ${{matrix.arch}}
-        run: ci/github/setup_bdde.sh
 
       - name: Setup Boost
+        run: source ci/github/install.sh
         env:
           B2_ADDRESS_MODEL: ${{matrix.address-model}}
           B2_COMPILER: ${{matrix.compiler}}
           B2_CXXSTD: ${{matrix.cxxstd}}
           B2_SANITIZE: ${{matrix.sanitize}}
           B2_STDLIB: ${{matrix.stdlib}}
+          # Optional. Variables set here (to non-empty) will override the top-level environment variables
+          B2_DEFINES: ${{matrix.defines}}
+          B2_VARIANT: ${{matrix.variant}}
+          B2_LINK: ${{matrix.link}}
           # More entries can be added in the same way, see the B2_ARGS assignment in ci/enforce.sh for the possible keys.
-          # B2_DEFINES: ${{matrix.defines}}
-          # Variables set here (to non-empty) will override the top-level environment variables, e.g.
-          # B2_VARIANT: ${{matrix.variant}}
           # Set the (B2) target(s) to build, defaults to the test folder of the current library
           # Can alternatively be done like this in the build step or in the build command of the build step, e.g. `run: B2_TARGETS=libs/$SELF/doc ci/build.sh`
           # B2_TARGETS: libs/foo/test//bar
-        run: source ci/github/install.sh
 
       - name: Setup coverage collection
         if: matrix.coverage
@@ -321,6 +322,9 @@ jobs:
           B2_TOOLSET: ${{matrix.toolset}}
           B2_CXXSTD: ${{matrix.cxxstd}}
           B2_ADDRESS_MODEL: ${{matrix.addrmd}}
+          B2_DEFINES: ${{matrix.defines}}
+          B2_VARIANT: ${{matrix.variant}}
+          B2_LINK: ${{matrix.link}}
 
       - name: Collect coverage
         shell: powershell
@@ -330,6 +334,9 @@ jobs:
           B2_TOOLSET: ${{matrix.toolset}}
           B2_CXXSTD: ${{matrix.cxxstd}}
           B2_ADDRESS_MODEL: ${{matrix.addrmd}}
+          B2_DEFINES: ${{matrix.defines}}
+          B2_VARIANT: ${{matrix.variant}}
+          B2_LINK: ${{matrix.link}}
 
       - name: Upload coverage
         if: matrix.coverage
@@ -378,12 +385,15 @@ jobs:
             rm -rf boost-ci-cloned
 
       - name: Setup Boost
+        run: ci/github/install.sh
         env:
           B2_COMPILER: ${{matrix.compiler}}
           B2_CXXSTD: ${{matrix.cxxstd}}
           B2_SANITIZE: ${{matrix.sanitize}}
           B2_STDLIB: ${{matrix.stdlib}}
-        run: ci/github/install.sh
+          B2_DEFINES: ${{matrix.defines}}
+          B2_VARIANT: ${{matrix.variant}}
+          B2_LINK: ${{matrix.link}}
 
       - name: Run tests
         run: ci/build.sh
@@ -422,14 +432,16 @@ jobs:
           repository: boostorg/boost-ci
           ref: master
           path: boost-ci-cloned
+
       - name: Get CI scripts folder
         run: |
             # Copy ci folder if not testing Boost.CI
             [[ "$GITHUB_REPOSITORY" =~ "boost-ci" ]] || cp -r boost-ci-cloned/ci .
             rm -rf boost-ci-cloned
+
       - name: Setup Boost
-        env: {B2_DONT_BOOTSTRAP: 1}
         run: source ci/github/install.sh
+        env: {B2_DONT_BOOTSTRAP: 1}
 
       - name: Run CMake tests
         run: |