• Remove redundant wording.
• Update MK_ARM_EABI entry to note it is the default.
• Reword the entry for r290910.
• Fix various wording nits.
• Remove redundant '[arch]' tags where they are already specified.
• Various rewordings.

Submitted by: theraven (first pass from his feedback)
Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation