Revert "Simplify build jobs with anchors (#2938)"

This reverts commit 13c9e2d27b.

I was sure this passed CI on my fork (it didn't) - however,
it is now giving syntax errors and they might not yet be supported:
https://github.community/t5/GitHub-Actions/Support-for-YAML-anchors/m-p/30336

.github/workflows/ci-push.yml

@@ -2,7 +2,13 @@ name: CI
 
 on: [push]
 
-.build-strategy: &build-strategy
+jobs:
+  
+# Build jobs
+# These jobs build each Racket component separately and tests on the component start as soon as each
+# component finishes building.
+
+  build-racketcgc:
     strategy:
       fail-fast: false
       matrix:
@@ -10,11 +16,13 @@ on: [push]
         cify: [cify, nocify]
           
     runs-on: ${{ matrix.os }}
-
     env:
       RACKET_EXTRA_CONFIGURE_ARGS: ""
     
-.build-setup-extra-flags: &build-setup-extra-flags
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        fetch-depth: 100
     - name: Setup OS specific configure args
       if:  runner.os == 'macOS'
       run: echo "::set-env name=RACKET_EXTRA_CONFIGURE_ARGS::--enable-macprefix $RACKET_EXTRA_CONFIGURE_ARGS"
@@ -24,21 +32,6 @@ on: [push]
     - name: Setup cify if disabled
       if: matrix.cify == 'nocify'
       run: echo "::set-env name=CIFY_OPTION::--disable-cify"
-
-jobs:
-  
-# Build jobs
-# These jobs build each Racket component separately and tests on the component start as soon as each
-# component finishes building.
-
-  build-racketcgc:
-    <<: *build-strategy
-    
-    steps:
-    - uses: actions/checkout@v1
-      with:
-        fetch-depth: 100
-    <<: *build-setup-extra-flags
     - name: Configuring Racket CGC
       working-directory: ./racket/src
       run: >
@@ -71,14 +64,32 @@ jobs:
         path: ../racketcgc-${{ matrix.os }}-${{ matrix.cify }}-x64_git${{ github.sha }}.tar.bz2
 
   build-racket3m:
-    <<: *build-strategy    
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-18.04, macos-latest]
+        cify: [cify, nocify]
+            
+    runs-on: ${{ matrix.os }}
+    
     needs: build-racketcgc
     
+    env:
+      RACKET_EXTRA_CONFIGURE_ARGS: ""
+    
     steps:
     - uses: actions/checkout@v1
       with:
         fetch-depth: 100
-    <<: *build-setup-extra-flags
+    - name: Setup OS specific configure args
+      if:  runner.os == 'macOS'
+      run: echo "::set-env name=RACKET_EXTRA_CONFIGURE_ARGS::--enable-macprefix $RACKET_EXTRA_CONFIGURE_ARGS"
+    - name: Setup cify if enabled
+      if: matrix.cify == 'cify'
+      run: echo "::set-env name=CIFY_OPTION::--enable-cify"
+    - name: Setup cify if disabled
+      if: matrix.cify == 'nocify'
+      run: echo "::set-env name=CIFY_OPTION::--disable-cify"
     - uses: actions/download-artifact@master
       with:
         name: racketcgc-${{ matrix.os }}-nocify-x64_git${{ github.sha }}
@@ -118,9 +129,17 @@ jobs:
         path: ../racket3m-${{ matrix.os }}-${{ matrix.cify }}-x64_git${{ github.sha }}.tar.bz2
 
   build-racketcs:
-    <<: *build-strategy
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-18.04, macos-latest]
+            
+    runs-on: ${{ matrix.os }}
     needs: build-racketcgc
     
+    env:
+      RACKET_EXTRA_CONFIGURE_ARGS: ""
+      
     steps:
     - uses: actions/checkout@v1
       with: