Stop using deprecated em++ env variable in Makefile

Author: sipa

Makefile

@@ -5,7 +5,7 @@ miniscript: $(HEADERS) $(SOURCES) main.cpp
 	g++ -O3 -g0 -Wall -std=c++17 -march=native -flto -Ibitcoin $(SOURCES) main.cpp -o miniscript
 
 miniscript.js: $(HEADERS) $(SOURCES) js_bindings.cpp
-	em++ -O3 -g0 -Wall -std=c++17 -fno-rtti -flto -Ibitcoin $(SOURCES) js_bindings.cpp -s WASM=1 -s FILESYSTEM=0 -s ENVIRONMENT=web -s DISABLE_EXCEPTION_CATCHING=0 -s EXPORTED_FUNCTIONS='["_miniscript_compile","_miniscript_analyze","_malloc","_free"]' -s EXTRA_EXPORTED_RUNTIME_METHODS='["cwrap","UTF8ToString"]' -o miniscript.js
+	em++ -O3 -g0 -Wall -std=c++17 -fno-rtti -flto -Ibitcoin $(SOURCES) js_bindings.cpp -s WASM=1 -s FILESYSTEM=0 -s ENVIRONMENT=web -s DISABLE_EXCEPTION_CATCHING=0 -s EXPORTED_FUNCTIONS='["_miniscript_compile","_miniscript_analyze","_malloc","_free"]' -s EXPORTED_RUNTIME_METHODS='["cwrap","UTF8ToString"]' -o miniscript.js
 
 wrapper.dot: wrapper.txt
 	(echo "digraph wrapper {"; cat wrapper.txt | sed -e 's/^ \+//g' | sed -e 's/ \+/ /g' | cut -d ' ' -f 2 | rev | sed -e 's/l/u/g' | sed -e 's/s/a/g' | sort | uniq | sed -e 's/\([a-z]\)/\1,\1/g' | sed -e 's/^[a-z]//g' | sed -e 's/,[a-z]$$//g' | sed -e 's/,\(.\)\(.\)/  \1 -> \2;\n/g' | sort | uniq | sed -e 's/u/"l\/u"/g' | sed -e 's/a/\"a\/s\"/g'; echo "}") >wrapper.dot