Build 32-bit Linux static binary in a 64-bit system

[ariya]

Docker facilitates a self-contained system to build PhantomJS static binary (#13822). This works well on a 64-bit system. With some tweaks, it is still possible to pull a 32-bit Docker image and produce 32-bit static binary. However, it is preferred to keep using the same official 64-bit Ubuntu 14.04 image to produce 32-bit binary.

[ariya]

Some tricks from https://developer.mozilla.org/en-US/docs/Compiling_32-bit_Firefox_on_a_Linux_64-bit_OS:

Method 1: Cross-compile using 64-bit compiler and libraries. This requires packages such as gcc-multilib (and a few others), as well as -m32 in the CFLAGS.

Method 2: Create a 32-bit environment using chroot.

[Vanuan]

Would be great to support symbols as well: http://phantomjs.org/crash-reporting.html

[ariya]

Obsoleted for now, since we want to use system-installed Qt and QtWebKit (see e.g. #15341).