fix Issue 10998 - compile-time postblit call check is incorrectly suppressed

In the pull request #1801, I had forgot to remove the *ungag* code. That was caused the incorrect gagging regression.
[trivial] fix fail341.d mistake

AFAICS, `@nocall` is a mistake of `@disable`.
fix Issue 10980 - static initialization of immutable structs with disabled postblit fails
Merge pull request #2541 from 9rnsr/fix10980

Issue 10998 (REG 2.063) & Issue Issue 10980 - fix for compile-time postblit  call check