ARROW-12836: [C++] Add support for newer IBM i
ARROW-12836: [C++] Add support for newer IBM i

Newer versions of IBM i have CMAKE_SYSTEM_PROCESSOR set to powerpc or powerpc64. Hence in the current release ARROW_CPU_FLAG  defaults to "x86" which makes the install fail.

Closes #10365 from mennosiek/master

Lead-authored-by: Menno Siekerman <6a6576fda6b230ff37aa4f84ec57b8ec4b2b7848@users.noreply.github.com>
Co-authored-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@cozmixng.org>
Signed-off-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>

cpcloud/arrow,wesm/arrow,apache/arrow,laurentgo/arrow,apache/arrow,cpcloud/arrow,kou/arrow,apache/arrow,laurentgo/arrow,apache/arrow,apache/arrow,wesm/arrow,apache/arrow,kou/arrow,icexelloss/arrow,apache/arrow,apache/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,apache/arrow,cpcloud/arrow,icexelloss/arrow,kou/arrow,laurentgo/arrow,cpcloud/arrow,laurentgo/arrow,icexelloss/arrow,cpcloud/arrow,apache/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,cpcloud/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,kou/arrow,kou/arrow,cpcloud/arrow,wesm/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,kou/arrow,icexelloss/arrow,cpcloud/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,wesm/arrow,apache/arrow,laurentgo/arrow,cpcloud/arrow,kou/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,cpcloud/arrow,apache/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,cpcloud/arrow,kou/arrow,icexelloss/arrow,wesm/arrow,apache/arrow,apache/arrow,kou/arrow