Improve the fix-its for -Wparentheses to ensure that the fix-it

suggestions follow recovery. Additionally, add a note to these
diagnostics which suggests a fix-it for changing the behavior to what
the user probably meant. Examples:

t.cpp:2:9: warning: & has lower precedence than ==; == will be evaluated first
      [-Wparentheses]
  if (i & j == k) {
        ^~~~~~~~
          (     )
t.cpp:2:9: note: place parentheses around the & expression to evaluate it first
  if (i & j == k) {
        ^
      (    )

t.cpp:14:9: warning: using the result of an assignment as a condition
without
      parentheses [-Wparentheses]
  if (i = f()) {
      ~~^~~~~
      (      )
t.cpp:14:9: note: use '==' to turn this assignment into an equality
comparison
  if (i = f()) {
        ^
        ==

llvm-svn: 92975