firefox -> 63.0 WIP diff

[coypu%sdf.org@localhost]

So, I am attempting to update, unsuccessfully because bugs.
Here's my interim diff
http://coypu.sdf.org/firefox-63.0.diff

Need to do something about clang not having __float128 on netbsd
for the purpose of generating bindings, I thought the
right file for this is servo/components/style/build_gecko.rs
but that didn't seem to work well.
(toolchain/53679)

Also mysteriously I get:
error[E0308]: mismatched types
  --> servo/components/style/gecko/snapshot_helpers.rs:63:42
   |
63 |         .find(|attr| attr.mName.mBits == name.as_ptr() as usize)
   |                                          ^^^^^^^^^^^^^^^^^^^^^^ expected u64, found usize

mBits is apparently defined in dom/base/nsAttrName.h
and usize should be the same thing as uintptr_t, so... no idea.
Rust configuration error?