[CI] Appveyor toolchain build fails because CMake detects different C and C++ compilers

[asfimport]

Build log: https://ci.appveyor.com/project/ApacheSoftwareFoundation/arrow/builds/34377790/job/f955ccj8irpgh565#L440

Caused by a recent CMake release 3.18.

Reporter: Krisztian Szucs / @kszucs
Assignee: Krisztian Szucs / @kszucs

PRs and other links:

• GitHub Pull Request #7865

_{Note: This issue was originally created as ARROW-9599. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 7865
#7865