swift234

fix <rdar://problem/18213320> enum with raw values that are too big are not diagnosed

On that testcase, we now generate:

t.swift:8:22: error: integer literal '123456' overflows when stored into 'UInt8'
  case tooFarByFar = 123456
                     ^
t.swift:7:8: error: integer literal '256' overflows when stored into 'UInt8'
  case twoHundredFiftySix
       ^

instead of spitting out some warnings with no source loc (which Xcode eats).


This patch:
 - Propagates source locations for literals when synthesizing code in various places,
   so we get the right diagnostic at the right spot.
 - Improves the constant folding SIL Pass to print the value overflowing, which is
   necessary for cases with an implicit value (like 256 above), and is general goodness
   for the QoI of the diagnostic anyway.



Swift SVN r27756