fix: bring back support for build-time env vars (#691)

Author: JakeChampion

src/compileApplicationToWasm.js

@@ -101,6 +101,7 @@ export async function compileApplicationToWasm(input, output, wasmEngine, enable
         env: {
           ENABLE_EXPERIMENTAL_HIGH_RESOLUTION_TIME_METHODS: enableExperimentalHighResolutionTimeMethods ? '1' : '0',
           ENABLE_PBL: enablePBL ? '1' : '0',
+          ...process.env
         }
       }
     );