[C++] Does not build on RISC-V natively

[asfimport]

In SetupCxxFlags.cmake, CMAKE_SYSTEM_PROCESSOR is not recognized and thus ARROW_CPU_FLAG is set to "x86". Which makes compilation to fail later with:

In file included from /build/arrow/src/apache-arrow-8.0.1/cpp/src/arrow/array/validate.cc:33:
In file included from /build/arrow/src/apache-arrow-8.0.1/cpp/src/arrow/util/utf8.h:32:
In file included from /build/arrow/src/apache-arrow-8.0.1/cpp/src/arrow/util/simd.h:37:
/usr/lib/clang/14.0.6/include/nmmintrin.h:14:2: error: "This header is only meant to be used on x86 and x64 architecture"
#error "This header is only meant to be used on x86 and x64 architecture"
^

Environment: Arch Linux riscv64
Reporter: Felix Yan
Assignee: Yibo Cai / @cyb70289

PRs and other links:

• GitHub Pull Request #13902

_{Note: This issue was originally created as ARROW-17440. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Can you try again with 9.0.0?

[asfimport]

Antoine Pitrou / @pitrou:
Also cc @cyb70289

[asfimport]

Felix Yan:
I have tried with current master (10.0.0) and it fails earlier in cmake:

-- System processor: riscv64
-- Arrow build warning level: PRODUCTION
CMake Error at cmake_modules/SetupCxxFlags.cmake:457 (message):
  SSE4.2 required but compiler doesn't support it.
Call Stack (most recent call first):
  CMakeLists.txt:494 (include)


-- Configuring incomplete, errors occurred!

The linked PR fixes this.

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 13902
#13902