[Ionic v4] ionic build --prod timeout

**Description:**
I'm getting a timeout every time I try to compile the app with the prod flag. The node daemon seems to be sleeping as well since there's no cpu usage.

**Steps to Reproduce:**
Run
ionic build --prod --engine browser
or
ionic cordova build android --prod

**Output:**
```
ionic build --prod --engine browser --verbose
ionic:cli-utils Terminal info: { tty: true, ci: false } +0ms
ionic:cli-utils CLI global options: { _: [ 'build' ], help: null, h: null, verbose: true, quiet: null, interactive: true, color: true, confirm: null, json: null, prod: true, engine: 'browser', project: null, '--': [] } +153ms
ionic:cli-utils:lib:environment Environment open. +0ms
ionic:cli-utils:lib:project Project type from config: ionic/angular 4 (angular) +0ms
ionic:cli-utils Project name: undefined +10ms
ionic:cli Context: { binPath: '/usr/lib/node_modules/ionic/bin/ionic', libPath: '/usr/lib/node_modules/ionic', execPath: '/mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4', version: '4.0.0' } +0ms
ionic:cli-utils:lib:hooks Looking for ionic:build:before npm script. +0ms
ionic:cli-utils:lib:project:angular:build Looking for ionic:build npm script. +0ms
> ng run app:build:production
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:compiler initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/compiler.js
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:parser initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/parser.js
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:compiler initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/compiler.js
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:parser initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/parser.js
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:compiler initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/compiler.js
Wed, 25 Jul 2018 18:34:12 GMT snapdragon:parser initializing /mnt/c/Users/marce/Documents/Code/xCode/lingusocial-ionic-v4/node_modules/snapdragon/lib/parser.js
```

**My `ionic info`:**

```

Ionic:

ionic (Ionic CLI) : 4.0.0 (/usr/lib/node_modules/ionic)
Ionic Framework : @ionic/angular 4.0.0-beta.0
@angular-devkit/core : 0.7.0-rc.2
@angular-devkit/schematics : 0.7.0-rc.2
@angular/cli : 6.0.8
@ionic/ng-toolkit : 1.0.0
@ionic/schematics-angular : 1.0.0

Cordova:

cordova (Cordova CLI) : 8.0.0
Cordova Platforms : none

System:

NodeJS : v9.11.2 (/usr/bin/node)
npm : 6.2.0
OS : Linux 4.4

Environment:

ANDROID_HOME : not set
```

**Other Information:**

Begin by reproducing the timeout with `ionic build --prod --engine browser --verbose` and compare it with `ionic cordova build android --prod`. Trace the CLI handoff to `ng run app:build:production`, starting where the verbose output stops around the Snapdragon initialization. Done means production builds complete instead of hanging, with the relevant command paths still working.

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