Fix uv__to_stat function on Nuttx with newer gcc

[galpeter]

With a newer arm gcc (5.0+) the _DEFAULT_SOURCE macro gets defined when the unix/fs.c file is built thus trying to access a set of stat struct members which are not defined on Nuttx.

By adding an extra check to see if the build is for Nuttx we can correctly select the stat conversion code path.

libtuv-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com

[galpeter]

Related issue: https://github.com/Samsung/iotjs/issues/1313

[yichoi]

LGTM