Ignore generated libsel4 headers.
libsel4: Turn seL4_MsgMaxLength into an enum.

This has no effect on the code, but makes this value visible as a named
constant in Isabelle when importing C sources. It avoids us having to reference
120 as a magic number in numerous proofs.
trivial: Fix string typos.
libsel4: Avoid implicit pointer coercion from 0.

Comparing a pointer against a literal without an explicit cast is not supported
by the C parser.

JIRA: VER-429
separate benchmark output by tabs instead of spaces such that it is easier to paste into spreadsheet programs
enable existing armv7 log buffer address for odriod-xu: tested, it works