MNT: Add Linux aarch64, ppc64, and macOS arm64 builds

* Add support for linux-aarch64, linux-ppc64le, and osx-arm64 builds.
   - Add python and cross-python as build requirements for cross-compilation.
     c.f. https://conda-forge.org/docs/maintainer/knowledge_base/#cross-compilation-examples
* Bump build number.

conda-forge.yml

@@ -1,3 +1,7 @@
+build_platform:
+  linux_aarch64: linux_64
+  linux_ppc64le: linux_64
+  osx_arm64: osx_64
 os_version:
   linux_64: cos7
 conda_forge_output_validation: true
@@ -8,3 +12,4 @@ conda_build:
   pkg_format: '2'
 bot:
   inspection: hint-all
+test: native_and_emulated

recipe/meta.yaml

@@ -11,7 +11,7 @@ source:
   sha256: bdcb529330730c4c364b79789620f33bafad8c2c854c1205ecc2d16511c0b690
 
 build:
-  number: 1
+  number: 2
   script:
     # FIXME: Avoid 'ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]' error on osx builds
     - export CFLAGS="$CFLAGS -Wno-implicit-function-declaration"  # [osx and x86]
@@ -22,6 +22,8 @@ requirements:
   build:
     - {{ compiler('c') }}
     - {{ stdlib('c') }}
+    - cross-python_{{ target_platform }}  # [build_platform != target_platform]
+    - python  # [build_platform != target_platform]
   host:
     - pip
     - python