stream: Fix MacOS build. fsync as alias for fdatasync. (#6882)

If fdatasync is not available, use fsync instead.

For some reason, fdatasync is available when using clang from Xcode, even though no declaration is present in headers.

configure.ac

@@ -548,6 +548,7 @@ asctime_r \
 chroot \
 ctime_r \
 explicit_memset \
+fdatasync \
 flock \
 ftok \
 funopen \

main/streams/plain_wrapper.c

@@ -58,6 +58,9 @@ extern int php_get_gid_by_name(const char *name, gid_t *gid);
 #define fdatasync fsync
 #else
 # define PLAIN_WRAP_BUF_SIZE(st) (st)
+# if !defined(HAVE_FDATASYNC)
+#  define fdatasync fsync
+# endif
 #endif
 
 /* parse standard "fopen" modes into open() flags */