Prerequisites:
An Apple machine with discrete GPU having more than 2GB of VRAM is needed to repro this bug.

Steps to repro:
1. Open attached project and 'ProgressiveLightmappingExample' scene;
2. In the Lighting window press 'Generate Lighting' button.

Expected result:
Baking on GPU completes successfully.

Actual result:
Errors:
- 'OpenCL Error. Falling back to CPU lightmapper. Error callback from context: CL_INVALID_KERNEL'

- 'OpenCL Error. Falling back to CPU lightmapper. Error callback from context: [CL_INVALID_KERNEL] : OpenCL Error : clEnqueueNDRangeKernel failed: invalid kernel 0x0'

and

- `OpenCL Error. Falling back to CPU lightmapper. Error callback from context: [CL_INVALID_BUILD_OPTIONS] : OpenCL Error : clBuildProgram failed: Invalid build options "-D APPLE -D USE_SAFE_MATH -cl-std=CL1.2 -I /Applications/2019.1/Unity 2019.1.0b1_83b3ba1f99df/Unity.app/Contents/Resources/OpenCL/kernels/"`

are shown. Baking backend falls back to CPU Lightmapper. See attached video.

Notes:
- Reproducible in 2019.1.0b1, 2019.2.0a2, 2019.3.0a2, 2019.3.0a3;
- Reproducible on every project that uses GPU PLM on OSX;
- Reproducible on AMD GPU;
- Reproducible only with GPU PLM; not reproducible with CPU PLM or Enlighten.
- Reproducible only when the path to the Unity Editor installation has space;
- Reproducible on OSX 10.13.3 and OSX 10.13.4; Not reproducible on Windows 10.