[GHC] #11185: runghc can't find ghc-stage2 on a Windows build

[GHC]

#11185: runghc can't find ghc-stage2 on a Windows build
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Build System      |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1621
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"05a5ebed916dc00bc5761224047440fefe10485e/ghc"
 05a5ebed/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="05a5ebed916dc00bc5761224047440fefe10485e"
 Fix runghc when $1_$2_SHELL_WRAPPER = NO

 When that variable isn't on (which is always the case on Windows),
 `runghc` naively attempts to invoke `ghc` by finding an executable
 simply named `ghc`. This won't work if `ghc` doesn't exist (e.g., if
 we're building GHC and using `ghc-stage2` instead). A simple fix is to
 test for the existence of `ghc` beforehand, and if that fails, fall back
 on `ghc-stage2`.

 Fixes #11185.

 Test Plan: ./validate

 Reviewers: austin, hvr, thomie, bgamari

 Reviewed By: thomie, bgamari

 Differential Revision: https://phabricator.haskell.org/D1621

 GHC Trac Issues: #11185
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11185#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler