[C++] Fix build for 32-bit MSYS2

[asfimport]

see mailing list thread https://lists.apache.org/thread.html/0fc5f7ffe4eb4e4aea931f0b26902d27305cf98829fb5c4a7375f2ab@%3Cdev.arrow.apache.org%3E

Reporter: Wes McKinney / @wesm
Assignee: Javier Luraschi / @javierluraschi

Related issues:

• [CI] Add jobs for 32-bit and 64-bit MinGW (relates to)
• [R] Enable package to be made available on CRAN (is related to)

PRs and other links:

• GitHub Pull Request #3443
• GitHub Pull Request #3693

_{Note: This issue was originally created as ARROW-4297. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
I've split CI work: https://issues.apache.org/jira/browse/ARROW-4353

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 3693
#3693