macos: prevent use of utimensat() and futimensat() on macOS

And turn the compiler warnings into errors so we don't use functions
that aren't supported on the targeted macOS version.

This should fix indygreg/PyOxidizer#112 once
a produced distribution makes its way to PyOxidizer.

Author: indygreg

cpython-unix/build-cpython.sh

@@ -107,6 +107,8 @@ CFLAGS="-fPIC -I${TOOLS_PATH}/deps/include -I${TOOLS_PATH}/deps/include/ncurses"
 
 if [ "${PYBUILD_PLATFORM}" = "macos" ]; then
     CFLAGS="${CFLAGS} -I${TOOLS_PATH}/deps/lib/libffi-3.2.1/include -I${TOOLS_PATH}/deps/include/uuid"
+    # Prevent using symbols not supported by current macOS SDK target.
+    CFLAGS="${CFLAGS} -Werror=unguarded-availability-new"
 fi
 
 CPPFLAGS=$CFLAGS
@@ -134,6 +136,13 @@ fi
 CFLAGS=$CFLAGS CPPFLAGS=$CFLAGS LDFLAGS=$LDFLAGS \
     ./configure ${CONFIGURE_FLAGS}
 
+# configure checks for the presence of functions and blindly uses them,
+# even if they aren't available in the target macOS SDK. Work around that.
+if [ "${PYBUILD_PLATFORM}" = "macos" ]; then
+    sed -i "" "s/#define HAVE_UTIMENSAT 1//g" pyconfig.h
+    sed -i "" "s/#define HAVE_FUTIMENS 1//g" pyconfig.h
+fi
+
 # Supplement produced Makefile with our modifications.
 cat ../Makefile.extra >> Makefile