WASM: Replace NO_EXIT_RUNTIME=0 with EXIT_RUNTIME=1

Get rid of double negation to make the configuration easier to understand.

Change-Id: I5dfe256c2ac2ef131c3db20dce9ff492c529a5b1
Reference: https://emscripten.org/docs/tools_reference/emcc.html
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

mkspecs/wasm-emscripten/qmake.conf

@@ -37,7 +37,7 @@ EMCC_COMMON_LFLAGS += \
     -s FULL_ES2=1 \
     -s FULL_ES3=1 \
     -s USE_WEBGL2=1 \
-    -s NO_EXIT_RUNTIME=0 \
+    -s EXIT_RUNTIME=1 \
     -s ERROR_ON_UNDEFINED_SYMBOLS=1 \
     -s EXTRA_EXPORTED_RUNTIME_METHODS=[\"UTF16ToString\",\"stringToUTF16\"] \
     --bind \