Revert "Add custom target to wrap around custom commands. (#1986)" (#1996)
Revert "Add custom target to wrap around custom commands. (#1986)" (#1996)

Breaks the build when using makefiles.  The ninja build is fine.

This reverts commit 67ebe3f7aebe73426a3bf9718dba56f051d75db5.
dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,antiagainst/SPIRV-Tools,antiagainst/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,dneto0/SPIRV-Tools,KhronosGroup/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,antiagainst/SPIRV-Tools,dneto0/SPIRV-Tools,pierremoreau/SPIRV-Tools,KhronosGroup/SPIRV-Tools,pierremoreau/SPIRV-Tools,dneto0/SPIRV-Tools,antiagainst/SPIRV-Tools