I think #24534 broke the MacOS SDK:
0guest@gnu /tmp/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers$ ls -al
1total 32
2drwxr-xr-x 4 guest users 4096 Apr 22 18:58 ./
3drwxrwxrwt 4 root root 4096 Apr 22 18:58 ../
4---x---r-- 1 guest users 127 Jan 1 1970 Entitlements.plist
5---x---r-- 1 guest users 4307 Jan 1 1970 SDKSettings.json
6---x---r-- 1 guest users 3597 Jan 1 1970 SDKSettings.plist
7drwxr-xr-x 4 guest users 4096 Jan 1 1970 System/
8drwxr-xr-x 7 guest users 4096 Jan 1 1970 usr/
Causing the guix build to fail with:
0checking for x86_64-apple-darwin-gcc... env -u C_INCLUDE_PATH -u CPLUS_INCLUDE_PATH -u OBJC_INCLUDE_PATH -u OBJCPLUS_INCLUDE_PATH -u CPATH -u LIBRARY_PATH /home/kvaciral/.guix-profile/bin/clang --target=x86_64-apple-darwin -mmacosx-version-min=10.15 -B/bitcoin/depends/x86_64-apple-darwin/native/bin -mlinker-version=609 -isysroot/bitcoin/depends/SDKs/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers -Xclang -internal-externc-isystem/gnu/store/v770rvqs8q21mbzwb3gkihr2glgn80am-clang-10.0.1/lib/clang/10.0.1/include -Xclang -internal-externc-isystem/bitcoin/depends/SDKs/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers/usr/include
1checking whether the C compiler works... no
2configure: error: in `/bitcoin/depends/work/build/x86_64-apple-darwin/libevent/2.1.12-stable-6395cab7fb6':
3configure: error: C compiler cannot create executables
4See `config.log' for more details
5make: *** [[funcs.mk:283](http://funcs.mk:283/): /bitcoin/depends/work/build/x86_64-apple-darwin/libevent/2.1.12-stable-6395cab7fb6/./.stamp_configured] Error 77
6make: Leaving directory '/bitcoin/depends'
7kvaciral@penumbra:~/projects/bitcoin$
Reported by @kvaciral.