CICD: Build: Enable *-pc-windows-gnu builds again (with 'stable')

All the referenced issues have been closed:
rust-lang/rust#47048
rust-lang/rust#53454
rust-lang/cargo#6754

Since we can (and should) use 'stable' on these targets too, we don't
need the TOOLCHAIN logic any longer, so remove it.

Author: Enselic

.github/workflows/CICD.yml

@@ -92,9 +92,9 @@ jobs:
           - { os: ubuntu-18.04   , target: x86_64-unknown-linux-musl   , use-cross: use-cross }
           - { os: ubuntu-16.04   , target: x86_64-unknown-linux-gnu    }
           - { os: macos-latest   , target: x86_64-apple-darwin         }
-          # - { os: windows-latest , target: i686-pc-windows-gnu         , use-cross: use-cross }  ## disabled; linker errors (missing '_imp____acrt_iob_func')
+          - { os: windows-latest , target: i686-pc-windows-gnu         , use-cross: use-cross }
           - { os: windows-latest , target: i686-pc-windows-msvc        }
-          # - { os: windows-latest , target: x86_64-pc-windows-gnu       , use-cross: use-cross }  ## disabled; linker errors (missing '_imp____acrt_iob_func')
+          - { os: windows-latest , target: x86_64-pc-windows-gnu       , use-cross: use-cross }
           - { os: windows-latest , target: x86_64-pc-windows-msvc      }
     steps:
     - name: Git checkout
@@ -110,10 +110,6 @@ jobs:
       id: vars
       shell: bash
       run: |
-        # toolchain
-        TOOLCHAIN="stable" ## default to "stable" toolchain
-        # * specify alternate TOOLCHAIN for *-pc-windows-gnu targets; gnu targets on Windows are broken for the standard *-pc-windows-msvc toolchain (refs: <https://github.com/rust-lang/rust/issues/47048>, <https://github.com/rust-lang/rust/issues/53454>, <https://github.com/rust-lang/cargo/issues/6754>)
-        case ${{ matrix.job.target }} in *-pc-windows-gnu) TOOLCHAIN="stable-${{ matrix.job.target }}" ;; esac;
         # staging directory
         STAGING='_staging'
         echo set-output name=STAGING::${STAGING}
@@ -214,7 +210,7 @@ jobs:
     - name: Install Rust toolchain
       uses: actions-rs/toolchain@v1
       with:
-        toolchain: ${{ steps.vars.outputs.TOOLCHAIN }}
+        toolchain: stable
         target: ${{ matrix.job.target }}
         override: true
         profile: minimal # minimal component installation (ie, no documentation)