I was trying to reach the breakpoint in bgrunv without success, until I passed -a to
dist bootstrap.
Then I hit the breakpoint.
Breakpoint 1, install (dir=<optimized out>) at cmd/dist/build.c:1062
1062 bgrunv(bstr(&path), CheckExit, &compile);
Looking at cmd/dist/build.c:cmdbootstrap I see you can pass either -a, -s or -v.