For some reason importing the photon target is pain free, but importing the 2019-03 results in the following problem:
session context was:(profile=TARGET_DEFINITION:file:/Users/marcus.hirt/hg/openjdk/jmc/jmc/releng/platform-definitions/platform-definition-2019-03/platform-definition-2019-03.target, phase=org.eclipse.equinox.internal.p2.engine.phases.Install, operand=null --> [R]org.eclipse.platform.sdk.executable.cocoa.macosx.x86_64 4.11.0.I20190307-0500, action=org.eclipse.equinox.internal.p2.touchpoint.natives.actions.ChmodAction).
The action chmod failed - file /Users/marcus.hirt/workspaces/2019-03/jmc/.metadata/.plugins/org.eclipse.pde.core/.install_folders/1560084039940/../MacOS/eclipse does not exist