Bump minimal clang to 16

.github/workflows/test-compile.yml

@@ -43,7 +43,7 @@ jobs:
           - ubuntu-latest
         compiler:
           # oldest supported
-          - 'clang-14'
+          - 'clang-16'
           - 'gcc-11'
           # newest, make sure to update maximum standard step to match
           - 'clang-22'
@@ -73,7 +73,6 @@ jobs:
         uses: aminya/setup-cpp@v1
         with:
           compiler: ${{ matrix.compiler }}
-          gcc: ${{ (matrix.os == 'ubuntu-latest' && matrix.compiler == 'clang-14') && '12' || '' }}
 
       - name: Tool versions
         shell: bash
@@ -81,11 +80,6 @@ jobs:
           $CC --version
           $CXX --version
 
-      - name: Fix clang-14 toolchain
-        if: matrix.os == 'ubuntu-latest' && matrix.compiler == 'clang-14'
-        run: |
-          echo 'CXXFLAGS=--gcc-toolchain=/usr -isystem /usr/include/c++/12 -isystem /usr/include/x86_64-linux-gnu/c++/12' >> $GITHUB_ENV
-
       # minimum standard
       - name: Build C++20
         shell: bash