Make the following patterns illegal:
if var x = ... {
...
}
guard var x = ... else {
...
}
while var x = ... {
...
}
And provide a replacement fixit 'var' -> 'let'.
rdar://problem/23172698
Swift SVN r32855
Otherwise, we'll fail to capture "locals" declared in top-level guard
statements. This led to an assertion failure in SILGen.
Depends on previous commit.
rdar://problem/21997265
Swift SVN r30812
