vlib: save signal handler data to global vbls

Turns out that clang is a bit too enthusiastic about mapping static
variables to registers, which makes it hard to extract (especially)
the faulting VA from an optimized core file.

Type: improvement

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I836e5d9695aeb4c5ee4a27f9565acf08ee4eaac0