[GHC] #15440: Flush eventlog in hs_init_ghc

[GHC]

#15440: Flush eventlog in hs_init_ghc
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           Reporter:  maoe           |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Runtime        |           Version:  8.4.3
  System                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Currently GHC RTS traces some basic information about the process in
 `hs_init_ghc` but the information is often flushed to the eventlog at the
 very end of the process lifetime. Or even worse, it's never written to it
 if the process terminates abnormally.

 This is very inconvenient because the information contains some useful
 stuff like EVENT_WALL_CLOCK_TIME, which is quite important if user wants
 to sync timestamps in the eventlog with clock.

 The simplest way to fix the issue is to flush the eventlog buffer in
 `hs_init_ghc`.

 This is implemented at
 https://github.com/maoe/ghc/commit/30e20e4e66adccc28c59c8876331918d30eacef2.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15440>
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