2nd attempt to fix T9032 test-case

First attempt via 7a2c9dde24b72f wasn't working properly. This attempt
should work better as it doesn't cause the makefile recipe to fail which
causes `make` to emit additional varying output.
Fix T9384: fix increacing capabilites number for eventlog.

Summary:
Event log had inconcistent support for increacing capabilies
number, as header were not inserted in capability buffer. It
resulted in a ghc-events crash (see #9384). This commit
fixes this issue by inserting required header when number
of capabilies grows.

Reviewers: simonmar, trofi, Mikolaj, austin

Subscribers: carter, thomie

Differential Revision: https://phabricator.haskell.org/D592

GHC Trac Issues: #9384