[NFC] Inclusive language: rename master flag to main flag

[NFC] As part of using inclusive language within the llvm project, this patch
renames master flag to main flag in these comments.

Reviewed By: ZarkoCA

Differential Revision: https://reviews.llvm.org/D114090

GitOrigin-RevId: b11c66accfb1d78324278072ed0069d3bbe835cd
1 file changed