while installing pycryptodome, the package is built from source. Because no toolchain is found build fails with the following error. To work around this issue temporarily i created a symlink MacOSX11.1.sdk -> MacOSX.sdk but it is not possible to do this on all machines.


```
 Compiling with an SDK that doesn't seem to exist: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk
  Please check your Xcode installation
  clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -arch x86_64 -mmacosx-version-min=10.9 -Wno-nullability-completeness -Wno-expansion-to-defined -Wno-undef-prefix -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -fPIC -I/var/folders/z1/xsh33bjd5d75qltcvxqy1gmm0000gp/T/tmpn5yvyhzp/tools/deps/include -I/var/folders/z1/xsh33bjd5d75qltcvxqy1gmm0000gp/T/tmpn5yvyhzp/tools/deps/include/ncursesw -I/var/folders/z1/xsh33bjd5d75qltcvxqy1gmm0000gp/T/tmpn5yvyhzp/tools/deps/include/uuid -Werror=unguarded-availability-new -g0 -DLTC_NO_ASM -DHAVE_UINT128 -DHAVE_CPUID_H -Isrc/ -I/Users/foo/.cache/_bazel_root/c7ac193d3d155e3d99f7f1334482aa2d/external/py39/dist/include/python3.9 -c src/MD2.c -o build/temp.macosx-10.9-x86_64-3.9/src/MD2.o
  clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk' [-Wmissing-sysroot]
  In file included from src/MD2.c:28:
  src/pycrypto_common.h:58:10: fatal error: 'stdlib.h' file not found
  #include <stdlib.h>
           ^~~~~~~~~~
  1 error generated.
  error: command '/usr/bin/clang'
~                                 
```