Update Emscripten-build-instructions.md

Author: mcbarton

Emscripten-build-instructions.md

@@ -131,7 +131,9 @@ emcmake cmake -DCMAKE_BUILD_TYPE=Release `
                         -DCLANG_BUILD_TOOLS=OFF                         `
                         -G Ninja `
                         ..\llvm
-$env:EMCC_CFLAGS="-Oz" emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
+$env:EMCC_CFLAGS="-Oz"
+emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
+$env:EMCC_CFLAGS=""
 ```
 
 on Windows. Once this finishes building we need to take note of where we built our llvm build. This can be done by executing the following on Linux and osx