[C++] System Apache ORC used detection is broken

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

arrow/cpp/src/arrow/CMakeLists.txt

Line 83 in 8dd9eba

if(ORC_SOURCE STREQUAL "SYSTEM")

uses ORC_SOURCE but we define orc_SOURCE.

Component(s)

C++

[raulcd]

Issue resolved by pull request 47915
#47915