"tsc watch" task broken for projects with references

[RomainMuller]

• VSCode Version: 1.30.2
• OS Version: macOS X 10.13.6 (17G4015)

Steps to Reproduce:

1. Open a package with references in the tsconfig.json file
2. Attempt to execute the tsc : watch - tsconfig.json build task
3. Behold the tsc error (pardon my french):

   > Executing task: tsc --watch -b /Repro/tsconfig.json <
   
   error TS6369: Option '--build' must be the first command line argument.
   Le processus du terminal s'est achevé avec le code de sortie 1
   
   Le terminal sera réutilisé par les tâches, appuyez sur une touche pour le fermer.
   

Does this issue occur when all extensions are disabled?: Yes

---

The issue appears to be caused by the -b being added at tasks.ts:221 and --watch being prepended to that value at tasks.ts:200, resulting in an invalid invocation of tsc. A possible solution might be to append --watch at the end instead of prepending.

[RomainMuller]

I have a fix for this in my fork that I should be able to push a PR for pretty soon (waiting for employee to approve the contrib).