watchman/thirdparty/jansson/load.cpp: avoid shadowing warnings
watchman/thirdparty/jansson/load.cpp: avoid shadowing warnings

Summary:
Fix warnings exposed by gcc-4.9.x's -Wshadow-compatible-local
I plan to enable this for all of fbcode, soon.
See https://fburl.com/bad-shadow for justification.

Move declarations of outer "value" down, past inner declaration, to where used.

This avoids the following errors:

  watchman/thirdparty/jansson/load.cpp:490:20: error: declaration of 'value' shadows a previous local [-Werror=shadow-compatible-local]
  watchman/thirdparty/jansson/load.cpp:465:12: error: shadowed declaration is here [-Werror=shadow-compatible-local]

Reviewed By: wez

Differential Revision: D4674209

fbshipit-source-id: c56ad7fdba92c9a2b11f878800edb22d641fae4b

nodakai/watchman,nodakai/watchman,kwlzn/watchman,kwlzn/watchman,facebook/watchman,facebook/watchman,kwlzn/watchman,kwlzn/watchman,wez/watchman,wez/watchman,facebook/watchman,wez/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,facebook/watchman,nodakai/watchman,wez/watchman,kwlzn/watchman,wez/watchman,nodakai/watchman,kwlzn/watchman,nodakai/watchman,kwlzn/watchman,facebook/watchman,nodakai/watchman