Fix XEUS_CPP_RESOURCE_DIR Emscripten-build-instructions.rst

Author: mcbarton

docs/Emscripten-build-instructions.rst

@@ -341,12 +341,13 @@ Assuming it passes all test you can install by executing the following.
 A project which makes use of the wasm build of CppInterOp is xeus-cpp.
 xeus-cpp is a C++ Jupyter kernel. Assuming you are in the CppInterOp
 build folder, you can build the wasm version of xeus-cpp by executing
-(replace $LLVM_VERSION with the version of llvm you are building against)
+(replace LLVM_VERSION with the version of llvm you are building against)
 
 .. code:: bash
 
    cd ../..
    git clone --depth=1 https://github.com/compiler-research/xeus-cpp.git
+   export LLVM_VERSION=20
    cd ./xeus-cpp
    mkdir build
    cd build
@@ -356,7 +357,7 @@ build folder, you can build the wasm version of xeus-cpp by executing
            -DCMAKE_INSTALL_PREFIX=$PREFIX                                 \
            -DXEUS_CPP_EMSCRIPTEN_WASM_BUILD=ON                            \
            -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON                         \
-	   -DXEUS_CPP_RESOURCE_DIR=$LLVM_BUILD_DIR/lib/clang/$LLVM_VERSION \
+	   -DXEUS_CPP_RESOURCE_DIR="$LLVM_BUILD_DIR/lib/clang/$LLVM_VERSION" \
            -DSYSROOT_PATH=$SYSROOT_PATH                                   \
            ..
    emmake make -j $(nproc --all) install