Fix build instructions and make start on xeus-cpp instructions

Author: mcbarton

Emscripten-build-instructions.md

@@ -1,6 +1,8 @@
-# CppInterOp Wasm Build
+# Wasm Build Instructions
 
-This document contains the instructions on how to build a wasm  
+## CppInterOp Wasm Build Instructions
+
+This document first starts with the instructions on how to build a wasm  
 build of CppInterOp. Before we start it should be noted that  
 unlike the non wasm version of CppInterOp we currently only  
 support the Clang-REPL backend using llvm>19 for osx and Linux.  
@@ -76,7 +78,14 @@ emmake make clang-repl -j $(nproc --all)
 emmake make lld -j $(nproc --all)
 ```
 
-Once this finishes building we can move onto building the wasm  
+Once this finishes building we need to take note of where we built our  
+llvm build. This can be done by executing the following
+
+```bash
+export LLVM_BUILD_DIR=$PWD
+```
+
+We can move onto building the wasm  
 version of CppInterOp. To do this execute the following  
 
 ```bash
@@ -92,4 +101,36 @@ emcmake cmake -DCMAKE_BUILD_TYPE=Release    \
                 -DBUILD_SHARED_LIBS=ON                      \
                 -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON            \
                 ../
+emmake make -j $(nproc --all)
+```bash
+
+Once this finishes building we need to take note of where we built our  
+llvm build. This can be done by executing the following
+
+```bash
+export CPPINTEROP_BUILD_DIR=$PWD
+```
+
+## Xeus-cpp-lite Wasm Build Instructions
+
+A project which makes use of the wasm build of CppInterOp. To build this  
+execute the following 
+
+```bash
+cd ../..
+git clone --depth=1 https://github.com/compiler-research/xeus-cpp.git
+cd ./xeus-cpp
+mkdir build
+cd build
+export CMAKE_PREFIX_PATH=${{ env.PREFIX }} 
+export CMAKE_SYSTEM_PREFIX_PATH=${{ env.PREFIX }} 
+emcmake cmake \
+          -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }}          \
+          -DCMAKE_PREFIX_PATH=${{ env.PREFIX }}             \
+          -DCMAKE_INSTALL_PREFIX=${{ env.PREFIX }}          \
+          -DXEUS_CPP_EMSCRIPTEN_WASM_BUILD=ON               \
+          -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON            \
+          -DCppInterOp_DIR="$CPPINTEROP_BUILD_DIR/lib/cmake/CppInterOp"  \
+          ..
+        emmake make -j $(nproc --all)
 ```bash