scipy: BUG: Build failure with Xcode 12

Xcode 12 for OS X was just released, and I can’t build scipy with it. The command pip3 install . -v --user fails, ending with

  error: Command "clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -I/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -DUSE_VENDOR_BLAS=1 -Iscipy/sparse/linalg/dsolve/SuperLU/SRC -I/private/var/folders/cp/n8wtqs490tq5psknff1hv9qr0000gn/T/pip-build-env-k4q2ai5g/overlay/lib/python3.8/site-packages/numpy/core/include -c scipy/sparse/linalg/dsolve/SuperLU/SRC/clacon2.c -o build/temp.macosx-10.15-x86_64-3.8/scipy/sparse/linalg/dsolve/SuperLU/SRC/clacon2.o -MMD -MF build/temp.macosx-10.15-x86_64-3.8/scipy/sparse/linalg/dsolve/SuperLU/SRC/clacon2.o.d" failed with exit status 1
  Building wheel for scipy (PEP 517): finished with status 'error'
  ERROR: Failed building wheel for scipy
Failed to build scipy
ERROR: Could not build wheels for scipy which use PEP 517 and cannot be installed directly

This may be the same issue as https://github.com/scipy/scipy/issues/12656 — at least the error at the end is the same — but that issue was closed while only providing the suggestion to use a different compiler.

I am using Xcode 12, plus homebrew’s Python 3.8, pip3, and gfortran. Unfortunately, I am really trying to figure out how to get this to build in Sage (sagemath.org), and using a gcc toolchain instead of clang would be, at the least, very inconvenient.