MFC r259873:

gcc: small enhancements for the arm support.

fixes GCC-PR target/31152

Obtained from:	gcc 4.3 (rev. r118461, 125973: GPLv2)
MFC r260204:
Assert that accounting for the pmap resident pages does not underflow.
MFC r260205:
Update the description for pmap_remove_pages() to match the modern
times.  Assert that the pmap passed to pmap_remove_pages() is only
active on current CPU.
[automated] Merge in upstream-github/stable/9