firefox still fails on 2020Q1, netbsd-8, amd64

[Greg Troxel <gdt%lexort.com@localhost>]

I am still unable to build firefox on the current stable branch (pkg_rr
says everything else is up to date).  I seem to get a rust exception:

  stack backtrace:
     0:        0x111e23da3 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h25011aa22366c224
     1:        0x111e3ebec - core::fmt::write::ha12ed658db114443
     2:        0x111e22f35 - std::io::Write::write_fmt::h4af7cba2d713a4ae
     3:        0x111e162b5 - std::panicking::default_hook::{{closure}}::h40c839a455b6e51f
     4:        0x111e15fa2 - std::panicking::default_hook::ha7b528c4c03e8cd7
     5:        0x111e1691d - std::panicking::rust_panic_with_hook::h722fcaa44a484079
     6:        0x111e16500 - rust_begin_unwind
     7:        0x111e1647b - std::panicking::begin_panic_fmt::h0b17ea86f4e16647
     8:        0x111c6a214 - build_script_build::build_gecko::generate_structs::hb694995a40d4dde4
     9:        0x111c6bdcc - build_script_build::main::ha21599d23ae0ba69
    10:        0x111c52913 - std::rt::lang_start::{{closure}}::h0f9289e317b742e9
    11:        0x111e163e3 - std::panicking::try::do_call::h57e2dd84001f09e2
    12:        0x111e2a0d7 - __rust_maybe_catch_panic
    13:        0x111e19d24 - std::rt::lang_start_internal::h970abedbe5975a66
    14:        0x111c6c7b2 - main
    15:        0x111c4faab - ___start

  warning: build failed, waiting for other jobs to finish...


that is inscrutable.


I don't know if this means rust on 8 is troubled, or firefox is turning
into Windows, or something else...