Linux: Build with use_static_cpp=yes by default

[akien-mga]

This enables -static-libgcc -static-libstdc++ which help make custom Linux
builds more portable (official builds have been using this option for years).

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Note: I need to do some tests before merging as for official builds on Ubuntu 14.04 i386 I'm actually not using those, I probably ran into issues in the past and forgot to document them...
https://github.com/godotengine/godot-build-scripts/blob/master/build-linux/build.sh#L15-L17

Edit: "Solved", see below.

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Note: Distro packagers should typically set this option to no to keep using the distro-provided shared libgcc and libstdc++. This option is only for builds that need to be shared with users on other distros (which is the main use case for custom Godot builds, but not the one Linux distro packages).

[hpvb]

LGTM

[akien-mga]

Note: I need to do some tests before merging as for official builds on Ubuntu 14.04 i386 I'm actually not using those, I probably ran into issues in the past and forgot to document them...

Ah I did document the issue in the commit log: godotengine/godot-build-scripts@3319757

The problem is that it seemed to cause crashes on Ubuntu 18.04 i386 for some reason: #31743 (comment).

[akien-mga]

I amended the commit to apply that change only to 64-bit, as we still need to figure out why it would crash on Ubuntu 18.04 i386 with that option. Likely a Ubuntu bug, but nasty enough not to make this the default for i386.

I was lazy so this outright forces use_static_cpp off for 32-bit, but making an architecture-specific option with different default values and still the possibility to override it is a bit of a pain.

[akien-mga]

Cherry-picked for 3.2.4.