MFC r270882, r270930:

  In ARM asm code, ensure that every ENTRY(foo) has a matching END(foo).
  The EABI unwind info requires a .fnend for every .fnstart, and newer
  binutils will complain about seeing two .fnstart in a row.  This change
  allows newer tools to compile our code.

  Do not generate unwind info in asm functions if _STANDALONE is defined.
  The .fnend op causes the assembler to emit RELOC references to unwind
  support functions that don't exist in libstand.

Approved by:	re(gjb)
MFC r271050: Disable DIAGNOSTIC on low-end ARM platforms.

Approved by:	re(gjb)
Bump __FreeBSD_version after SA-14:18

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation