Fix non-Linux build failure.

gcc-preinclude.h contains a fix for old Linux systems but it's included
unconditionally on other platforms as well.

I could update the GYP files to exclude it on other platforms but it
seems easier to add a `defined(__linux__)` guard to the header file.

Let this be the last fix.

Fix non-x86 build failure.

The inclusion of gcc-preinclude.h breaks the build on ARM and i386
because of the missing .symver symbol.  Only define it on x86_64.

Closes out mapbox/node-sqlite3#445.

Fix glibc missing symbol errors

Pre-include gcc-preinclude.h in a few more places to ensure that we
don't pick up a reference to the memcpy@@GLIBC_2.14 symbol.

Fixes add-on loading on systems with an old glibc, such as RHEL <= 6.

Closes out mapbox/node-sqlite3#433.

Fixes the build with io.js v2.0.0.

Test key versions

Upgrade to nan@1.5.0 / Fix compile against io.js

Windows, Linux, Mac builds for yesterday's node-webkit (v0.11.5)