github/workflows: add more build matrix options

Use the revamped environment variables support in the makefile
to build and test all permutations of compilers and linkers,
including the default ones on the system. Also test the embed
tool's support for mold's spare program headers feature.

.github/workflows/lone.yml

@@ -12,17 +12,43 @@ jobs:
       fail-fast: false
       matrix:
         compiler:
-          - gcc
-          - clang
+          - name: cc
+            env:
+              CC: cc
+          - name: gcc
+            env:
+              CC: gcc
+          - name: clang
+            env:
+              CC: clang
+        linker:
+          - name: ld
+            env:
+              LD: ld
+          - name: lld
+            env:
+              LD: lld
+          - name: mold
+            env:
+              LD: mold
+          - name: mold+spare-segments
+            env:
+              LD: mold
+              LDFLAGS: -Wl,--spare-program-headers,2
     runs-on: ubuntu-latest
     container: archlinux:base-devel
     steps:
     - name: Set up pacman keys
       run: pacman-key --init
     - name: Update and install packages
-      run: pacman -Syu --noconfirm clang
+      run: pacman -Syu --noconfirm clang lld llvm mold
     - uses: actions/checkout@v4
     - name: Build
-      run: make CC=${{ matrix.compiler }}
+      run: make
+      env:
+        CC: ${{ matrix.compiler.env.CC }}
+        LD: ${{ matrix.linker.env.LD }}
+        CFLAGS: ${{ matrix.compiler.env.CFLAGS }}
+        LDFLAGS: ${{ matrix.linker.env.LDFLAGS }}
     - name: Test
       run: make test