Fix multiple vulnerabilities in file(1) and libmagic(3).

Security:	FreeBSD-SA-14:16.file
Approved by:	so
MFC 253392:
Workaround some broken BIOSes that specify edge-sensitive but active-low
settings for ACPI-enumerated serial ports by forcing any IRQs that use
an ISA IRQ value with these settings to active-high instead of active-low.

This is known to occur with the BIOS on an Intel D2500CCE motherboard.
MFC: r224269

Add missing XHCI early takeover code. The XHCI takeover code
is supposed to disable the BIOS from using the XHCI controller
after bootup.
MFC 266296:
Correct some minor nits in the per-thread signal format description such
as missing posessives and misordering of fields.