Xcode: Add "inputPaths" to custom command script build phase

Since commit v3.9.0~3^2 (Xcode: Add "outputPaths" to custom command
script build phase, 2017-07-13) Xcode will only re-run the custom
build phase if its outputs are missing.  Add the inputs too.

Fixes: #17178
Status Job ID Name Coverage
  External
passed ghostflow-branch-check-master

passed ghostflow-commit-check