[C++] Failed building on LoongArch platform

[liujiacheng777]

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

loongson@loongson-pc:~/tmp/arrow/cpp/build$ arch
loongarch64
loongson@loongson-pc:~/tmp/arrow/cpp/build$ cmake ..
-- Building using CMake version: 3.13.4
-- The C compiler identification is GNU 8.3.0
-- The CXX compiler identification is GNU 8.3.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Arrow version: 12.0.0 (full: '12.0.0-SNAPSHOT')
-- Arrow SO version: 1200 (full: 1200.0.0)
-- clang-tidy 14 not found
-- clang-format 14 not found
-- Could NOT find ClangTools (missing: CLANG_FORMAT_BIN CLANG_TIDY_BIN) 
-- infer not found
-- Found Python3: /usr/local/bin/python3.8 (found version "3.8.2") found components:  Interpreter 
-- Found cpplint executable at /home/loongson/tmp/aa/arrow/cpp/build-support/cpplint.py
-- System processor: loongarch64
CMake Error at cmake_modules/SetupCxxFlags.cmake:40 (message):
  Unknown system processor
Call Stack (most recent call first):
  CMakeLists.txt:416 (include)


-- Configuring incomplete, errors occurred!
See also "/home/loongson/tmp/aa/arrow/cpp/build/CMakeFiles/CMakeOutput.log".

loongson@loongson-pc:~/tmp/arrow/cpp/build$ make
In file included from /home/loongson/tmp/aa/arrow/cpp/src/arrow/vendored/double-conversion/double-conversion.h:31,
                 from /home/loongson/tmp/aa/arrow/cpp/src/arrow/util/double_conversion.h:20,
                 from /home/loongson/tmp/aa/arrow/cpp/src/arrow/util/formatting.h:35,
                 from /home/loongson/tmp/aa/arrow/cpp/src/arrow/pretty_print.cc:41:
/home/loongson/tmp/aa/arrow/cpp/src/arrow/vendored/double-conversion/utils.h:118:2: error: #error Target architecture was not detected as supported by Double-Conversion.
 #error Target architecture was not detected as supported by Double-Conversion.
  ^~~~~
make[2]: *** [src/arrow/CMakeFiles/arrow_objlib.dir/build.make:466：src/arrow/CMakeFiles/arrow_objlib.dir/pretty_print.cc.o] 错误 1
make[1]: *** [CMakeFiles/Makefile2:684：src/arrow/CMakeFiles/arrow_objlib.dir/all] 错误 2
make: *** [Makefile:141：all] 错误 2

Component(s)

C++