8284539: Configure --with-source-date=version fails on MacOS

Reviewed-by: erikj, ihse

make/autoconf/util.m4

@@ -239,12 +239,17 @@ AC_DEFUN([UTIL_GET_EPOCH_TIMESTAMP],
     timestamp=$($DATE --utc --date=$2 +"%s" 2> /dev/null)
   else
     # BSD date
-    timestamp=$($DATE -u -j -f "%FZ %TZ" "$2" "+%s" 2> /dev/null)
+    # ISO-8601 date&time in Zulu 'date'T'time'Z
+    timestamp=$($DATE -u -j -f "%FT%TZ" "$2" "+%s" 2> /dev/null)
     if test "x$timestamp" = x; then
       # BSD date cannot handle trailing milliseconds.
       # Try again ignoring characters at end
       timestamp=$($DATE -u -j -f "%Y-%m-%dT%H:%M:%S" "$2" "+%s" 2> /dev/null)
     fi
+    if test "x$timestamp" = x; then
+      # Perhaps the time was missing.
+      timestamp=$($DATE -u -j -f "%FT%TZ" "$2""T00:00:00Z" "+%s" 2> /dev/null)
+    fi
   fi
   $1=$timestamp
 ])