Build.sh hangs on MINGW64 Bash Shell #12454

I'm submitting a ... (check one with "x")

[x] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[ ] support request

Current behavior
Execution of build.sh hangs on the MINGW64 bash shell provided with Git for Windows. The script loops over packages in the @angular directory building each in turn. The hang occurs when uglify is called against the first package - I see the warnings about unreachable code then nothing but a cursor. Running the script in bash's debug mode confirms the call to uglify is the last to be made. Node.exe memory usage stays very low and does not fluctuate.

This is where the issue gets weird:

1. I got the build to complete yesterday
2. I can resolve the issue by changing line 160 from

    ) 2>&1 | grep -v "as external dependency"

to

    ) 2>&1

The downside of this is you get more noise in the terminal - but it hasn't hung a single time. The tests seem to all pass afterward as well. As soon as I change the line back - the script hangs every time.

Expected behavior
New devs can get build.sh to reliably complete. If a change isn't committed then maybe a note should be added to the dev guide.

Minimal reproduction of the problem with instructions
Build on windows using the Git for Windows bash shell. (You will need the fixes from my other 2 PRs to get past other problems)

What is the motivation / use case for changing the behavior?
Removing obstacles in the way of new contributors building the project is good.

Please tell us about your environment:
Windows 10, Git for Windows 2.8.1.windows., Node v5.12.0, NPM v3.10.8

• Angular version: 2.0.X
  Angular Master from 2 days ago.
• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
  N/A
• Language: [all | TypeScript X.X | ES6/7 | ES5]
  N/A
• Node (for AoT issues): node --version =
  Node v5.12.0