MFC	r259920:

gcc: Implement -Wmost for compatibility with clang.

This is equivalent to -Wall -Wno-parentheses.

Obtained from:	Apple GCC 4.2 - 5531
Revert unrelated fix that went into r260569.

The fix is good but the minimum MFC period for this change
has not elapsed yet.
MFC	r260310:

libcpp: misc fixes from Apple's GCC.

Fixes some bugs detected by Apple:
  #error with unmatched quotes
  pragma mark

Obtained from:	Apple GCC 4.2 - 5553
MFC r244607 and r244650:
Fix regression issues after r244503.

PR:	usb/185628
[automated] Merge in upstream-github/stable/9