newlib: Support both namespace protected & nonprotected stubs

Some variants of newlib build and expect namespace protected stubs
(typically having an underscore prefix).  To support such newlib variants
change all the stubs to the namespace protect version and use function
aliases to support the nonprotected namespace version.

Change-Id: I6a4162eca949afec96b152ffe6f60b87c4496c4d
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>