Improve the selection of headers included in the precompiled header.
This reduces build time of the full `io/usd` directory by 12 to 19%.
Laptop i7-8750h: Average 30.3 sec --> 24.5 sec
Desktop i7-13700k: Average 12.1 sec --> 10.7 sec
Pull Request: https://projects.blender.org/blender/blender/pulls/140418
9353fc280d