build: Fix non-PCH build on Linux and add non-PCH verification to CI. (#7351)

.ci/linux.sh

@@ -1,7 +1,11 @@
 #!/bin/bash -ex
 
 if [ "$TARGET" = "appimage" ]; then
-    export COMPILER_FLAGS=(-DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_LINKER=/etc/bin/ld.lld)
+    # Compile the AppImage we distribute with Clang.
+    export EXTRA_CMAKE_FLAGS=(-DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_LINKER=/etc/bin/ld.lld)
+else
+    # For the linux-fresh verification target, verify compilation without PCH as well.
+    export EXTRA_CMAKE_FLAGS=(-DCITRA_USE_PRECOMPILED_HEADERS=OFF)
 fi
 
 mkdir build && cd build
@@ -9,7 +13,7 @@ cmake .. -G Ninja \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_C_COMPILER_LAUNCHER=ccache \
     -DCMAKE_CXX_COMPILER_LAUNCHER=ccache \
-    "${COMPILER_FLAGS[@]}" \
+    "${EXTRA_CMAKE_FLAGS[@]}" \
     -DENABLE_QT_TRANSLATION=ON \
     -DCITRA_ENABLE_COMPATIBILITY_REPORTING=ON \
     -DENABLE_COMPATIBILITY_LIST_DOWNLOAD=ON \