Avoid illegal definition of snprintf in VS 2015

Avoid illegal definition of snprintf in VS 2015

VS 2015 supplies an implementation of snprintf which makes definining
it to _snprintf illegal - previously it was just a really bad idea.
This reinstates the compiler version check so that libxml will compile
in Chromium.

README.chromium was also updated to make it explicit that these checks
need to be added (for now) when config.h is copied.

A corresponding change will need to be made upstream.

BUG=440500, 591920
Review URL: https://codereview.chromium.org/1770093002

Cr-Commit-Position: refs/heads/master@{#379755}
(cherry picked from commit f7bd300e8c52d6ebb7575a28d4cd9d3bdccaf439)

Committed: https://chromium.googlesource.com/chromium/src/+/40ff9d7fda350ccb83c171c68b60290d6ff3b74d

[dominicc (has gone to gerrit), 2016-03-28 12:48:52]

Description was changed from

==========
Avoid illegal definition of snprintf in VS 2015

VS 2015 supplies an implementation of snprintf which makes definining
it to _snprintf illegal - previously it was just a really bad idea.
This reinstates the compiler version check so that libxml will compile
in Chromium.

README.chromium was also updated to make it explicit that these checks
need to be added (for now) when config.h is copied.

A corresponding change will need to be made upstream.

BUG=440500,591920

Review URL: https://codereview.chromium.org/1770093002

Cr-Commit-Position: refs/heads/master@{#379755}
(cherry picked from commit f7bd300e8c52d6ebb7575a28d4cd9d3bdccaf439)
==========

to

==========
Avoid illegal definition of snprintf in VS 2015

VS 2015 supplies an implementation of snprintf which makes definining
it to _snprintf illegal - previously it was just a really bad idea.
This reinstates the compiler version check so that libxml will compile
in Chromium.

README.chromium was also updated to make it explicit that these checks
need to be added (for now) when config.h is copied.

A corresponding change will need to be made upstream.

BUG=440500,591920

Review URL: https://codereview.chromium.org/1770093002

Cr-Commit-Position: refs/heads/master@{#379755}
(cherry picked from commit f7bd300e8c52d6ebb7575a28d4cd9d3bdccaf439)

Committed:
https://chromium.googlesource.com/chromium/src/+/40ff9d7fda350ccb83c171c68b60...
==========

[dominicc (has gone to gerrit), 2016-03-28 12:48:55]

Committed patchset #1 (id:1) manually as
40ff9d7fda350ccb83c171c68b60290d6ff3b74d.