Examples: Properly append LDFLAGS to LD command

The LD command in examples/standalone/Makefile ignored platform specific
LDFLAGS setup. Pass these LDFLAGS to the command.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Bryan Hundven <bryanhundven@gmail.com>
Cc: Michael Schwingen <rincewind@discworld.dascon.de>