secp256k1: Segfault running make check with macOS 10.15 SDK (default for Catalina)

This also impacts running the test suite on Bitcoin Core:

% ./autogen.sh
...
% ./configure
...
Build Options:
  with endomorphism       = no
  with ecmult precomp     = yes
  with external callbacks = no
  with jni                = no
  with benchmarks         = yes
  with coverage           = no
  module ecdh             = no
  module recovery         = no

  asm                     = x86_64
  bignum                  = gmp
  field                   = 64bit
  scalar                  = 64bit
  ecmult window size      = 15
  ecmult gen prec. bits   = 4

  CC                      = gcc
  CFLAGS                  = -g -O2 -W -std=c89 -pedantic -Wall -Wextra -Wcast-align -Wnested-externs -Wshadow -Wstrict-prototypes -Wno-unused-function -Wno-long-long -Wno-overlength-strings -fvisibility=hidden -O3
  CPPFLAGS                = 
  LDFLAGS                 = 

% make
...
% make check
/Applications/Xcode.app/Contents/Developer/usr/bin/make  check-TESTS
./build-aux/test-driver: line 107: 70234 Segmentation fault: 11  "$@" > $log_file 2>&1
FAIL: tests
PASS: exhaustive_tests
============================================================================
Testsuite summary for libsecp256k1 0.1
============================================================================
# TOTAL: 2
# PASS:  1
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
============================================================================
See ./test-suite.log
============================================================================
make[2]: *** [test-suite.log] Error 1
make[1]: *** [check-TESTS] Error 2
make: *** [check-am] Error 2