ci: the shared suite, both architectures, and the toolchain named once

Author: Sunrisepeak

.github/workflows/ci.yml

@@ -70,10 +70,23 @@ jobs:
           mcpp --version
           mcpp self config --mirror GLOBAL
 
+      # The compiler family and version for this row. mcpp keeps its toolchains
+      # in a sandbox of its own, so this selects rather than installs into the
+      # system, and `mcpp test' and `mcpp run' have no flag for it --- which is
+      # why it is set once here rather than passed to each command.
+      - name: Select the toolchain
+        run: |
+          spec='${{ matrix.toolchain }}'
+          case "$spec" in
+            msvc*) mcpp toolchain default msvc ;;
+            *)     mcpp toolchain install "${spec%@*}" "${spec#*@}"
+                   mcpp toolchain default "$spec" ;;
+          esac
+          mcpp toolchain list
+
       - name: Every interface, every kind of examination
         run: |
-          bash .spec/tools/run-conformance.sh openkal-macos . full \
-            --toolchain '${{ matrix.toolchain }}'
+          bash .spec/tools/run-conformance.sh openkal-macos . full
 
       - name: The exported surface is complete and contains nothing else
         run: |
@@ -82,7 +95,7 @@ jobs:
           # source. --complete because this implementation claims every
           # interface: a name it fails to export is a failure, not an interface
           # it declines to provide.
-          rm -rf target && mcpp build --toolchain '${{ matrix.toolchain }}'
+          rm -rf target && mcpp build
           objs="$(find target -path '*/obj/*' -name '*.o' ! -name '*.m.o' | tr '\n' ' ')"
           test -n "$objs" || { echo "no objects were found" >&2; exit 1; }
           bash .spec/tools/check-surface.sh --complete .spec/SURFACE.txt $objs
@@ -92,7 +105,7 @@ jobs:
       # library through a macro.
       - name: The objects reference nothing of a C library but the two named
         run: |
-          rm -rf target && mcpp build --features standalone --toolchain '${{ matrix.toolchain }}'
+          rm -rf target && mcpp build --features standalone
           objs="$(find target -path '*/obj/*' -name '*.o' ! -name '*.m.o')"
           test -n "$objs" || { echo "no objects were found; the check would pass vacuously" >&2; exit 1; }
 
@@ -126,7 +139,7 @@ jobs:
       - name: The independence check detects a dependence
         run: |
           printf 'extern "C" int puts(const char*);\nextern "C" void okm_probe(void) { puts("x"); }\n' > src/probe.cpp
-          rm -rf target && mcpp build --features standalone --toolchain '${{ matrix.toolchain }}'
+          rm -rf target && mcpp build --features standalone
           objs="$(find target -path '*/obj/*' -name '*.o' ! -name '*.m.o')"
           if ! nm -u $objs | sed 's/^ *//' | grep -qx '_puts'; then
             echo "the probe did not produce the reference it was written to produce" >&2