Support multiple Targets in Podfile (error: Pods already has a platform set)

[buddhisthead]

If I have multiple targets in my Podfile, then I see an error during pod install

A Podfile with multiple Targets (watchOS, iOS, testing) that each define their platform will results in an error, though this is quite important to support. Thank you.

[!] Invalid `Podfile` file: The target `Pods` already has a platform set..

 #  from [redacted]/MergeCache/Podfile:4
 #  -------------------------------------------
 #  platform :ios, '11.0'
 >  platform :watchos, '3.1'
 #  install! 'cocoapods', :integrate_targets => false, :lock_pod_sources => false
 #  -------------------------------------------