unix: don't redefine HMAC symbols when using LibreSSL

This works around a redefinition of symbols exported by LibreSSL's
libcrypto. I filed https://bugs.python.org/issue41949 upstream to
track this.

cpython-unix/build-cpython.sh

@@ -218,6 +218,27 @@ EOF
 sed s/__APPLE__/USE_LIBEDIT/g Modules/readline-libedit.c > tmp
 mv tmp Modules/readline-libedit.c
 
+# Modules/_hashopenssl.c redefines some libcrypto symbols on Python 3.9 and
+# this makes the linker unhappy. So rename the symbols to work around.
+# https://bugs.python.org/issue41949.
+if [ "${PYTHON_MAJMIN_VERSION}" = "3.9" ]; then
+    patch -p1 <<EOF
+diff --git a/Modules/_hashopenssl.c b/Modules/_hashopenssl.c
+index adc8653773..fc9070fc21 100644
+--- a/Modules/_hashopenssl.c
++++ b/Modules/_hashopenssl.c
+@@ -32,7 +32,7 @@
+ #  error "OPENSSL_THREADS is not defined, Python requires thread-safe OpenSSL"
+ #endif
+
+-#if (OPENSSL_VERSION_NUMBER < 0x10100000L) || defined(LIBRESSL_VERSION_NUMBER)
++#if (OPENSSL_VERSION_NUMBER < 0x10100000L)
+ /* OpenSSL < 1.1.0 */
+ #define EVP_MD_CTX_new EVP_MD_CTX_create
+ #define EVP_MD_CTX_free EVP_MD_CTX_destroy
+EOF
+fi
+
 # Most bits look at CFLAGS. But setup.py only looks at CPPFLAGS.
 # So we need to set both.
 CFLAGS="${EXTRA_TARGET_CFLAGS} -fPIC -I${TOOLS_PATH}/deps/include -I${TOOLS_PATH}/deps/include/ncursesw"