Don't use the non-public fdatasync() API when sandboxed on macOS

Change-Id: I9e36cb78e3e945f6531a31e0ddf73d9c8d655f7d
diff --git a/external/apr/ExternalProject_apr.mk b/external/apr/ExternalProject_apr.mk
index 093cdde..00e3ab6 100644
--- a/external/apr/ExternalProject_apr.mk
+++ b/external/apr/ExternalProject_apr.mk
@@ -26,6 +26,7 @@ $(call gb_ExternalProject_get_state_target,apr,build):
else
$(call gb_ExternalProject_get_state_target,apr,build):
	+$(call gb_ExternalProject_run,build,\
		 $(if $(ENABLE_MACOSX_SANDBOX),ac_cv_func_fdatasync=no) \
		./configure \
			--enable-static --disable-shared \
			--with-pic \