Fix errors caused by illegal #define of snprintf.

Fix errors caused by illegal #define of snprintf.

Because VS has, for a long time, not had snprintf some developers have
fixed this with #define snprintf _snprintf. This is scary because the
two functions behave differently, and it also breaks with VS 2015 which
does implement snprintf. So, the #defines all need a version check.

The errors are:

stdio.h(1926): warning C4005: 'snprintf': macro redefinition
libxml\win32\config.h(98): note: see previous definition of 'snprintf'
libxml\src\include\win32config.h(98): note: see previous def of 'snprintf'
stdio.h(1929): fatal error C1189: #error:  Macro definition of snprintf
conflicts with Standard Library function declaration

R=cpu@chromium.org
BUG=440500
Committed: https://crrev.com/548cc22b487981ecd15a2e0b869a15309446e6f4
Cr-Commit-Position: refs/heads/master@{#325832}

[cpu_(ooo_6.6-7.5), 2015-04-09 00:33:49]

lgtm but same deal you need to add the patch to \patches

[brucedawson, 2015-04-16 20:41:18]

Patches and README.chromium changes made.

PTAL.

[brucedawson, 2015-04-20 10:54:18]

The CQ bit was checked by brucedawson@chromium.org

[brucedawson, 2015-04-20 10:54:18]

The patchset sent to the CQ was uploaded after l-g-t-m from cpu@chromium.org
Link to the patchset: https://codereview.chromium.org/1072653003/#ps40001
(title: "Change tense of comment.")

[commit-bot: I haz the power, 2015-04-20 10:54:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1072653003/40001

[commit-bot: I haz the power, 2015-04-20 12:09:30]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-04-20 12:10:20]

Patchset 3 (id:??) landed as
https://crrev.com/548cc22b487981ecd15a2e0b869a15309446e6f4
Cr-Commit-Position: refs/heads/master@{#325832}