py-pyarrow: fix build for aarch64 (#20335)

var/spack/repos/builtin/packages/py-pyarrow/for_aarch64.patch

@@ -0,0 +1,14 @@
+--- spack-src/CMakeLists.txt.bak	2020-05-14 19:42:00.000000000 +0900
++++ spack-src/CMakeLists.txt	2020-12-11 14:02:52.645857641 +0900
+@@ -97,6 +97,11 @@
+ # Cython generated code emits way to many warnings at CHECKIN and EVERYTHING
+ set(BUILD_WARNING_LEVEL "PRODUCTION")
+ 
++# This must be synchronized with the definition in
++# cmake_modules/DefineOptions.cmake.
++set(ARROW_ARMV8_ARCH
++    "armv8-a"
++    CACHE STRING "Arm64 arch and extensions: armv8-a, armv8-a or armv8-a+crc+crypto")
+ include(SetupCxxFlags)
+ 
+ # Add common flags

var/spack/repos/builtin/packages/py-pyarrow/package.py

@@ -49,6 +49,8 @@ class PyPyarrow(PythonPackage, CudaPackage):
 
     phases = ['build_ext', 'install']
 
+    patch('for_aarch64.patch', when='target=aarch64:')
+
     def build_ext_args(self, spec, prefix):
         args = []
         if spec.satisfies('+parquet'):