v8: fix for change in Error api

Before v8 3.16.6 the error stack message was lazily written when it was
needed, but that has changed. Now it creates that stack message on
instantiation, and doesn't rewrite the message if a new message is set.

This is not a complete fix for the problem. Getting error without any
message isn't very useful.
v8: revert dtrace fix from 3.14 downgrade

Revert "v8: fix postmortem and dtrace helper build"

This reverts commit aa985392777dbe6159ce4ca56ae79d1039e43ec7.
dtrace: fix style in ustack helper
dtrace: x64 ustack helper
dtrace: Make D style more D-ish
dtrace: More style

Continuation lines should be indented with 4 spaces, not a tab.
dtrace: fix generation of v8 constants on freebsd

Every constant is certainly 4 bytes now, but freebsd's objdump utility
prints out odd byte sequences (5-bytes, 6-bytes and even 9-bytes long)
for v8's data section. We can safely ignore all upper bytes, because all
constants that we're using are just `int`s. Since on all supported
platforms `int` is 32bit long (and anyway v8's constants are 32bit too),
we ignore all higher bits if they were read.