Neil pointed out that clang doesn't generate ranges from diagnostics

related to pp-expressions.  Doing so is pretty simple and this
patch implements it, yielding nice diagnostics like:

t.c:2:7: error: division by zero in preprocessor expression
#if 1 / (0 + 0)
    ~ ^ ~~~~~~~
t.c:5:14: error: expected ')' in preprocessor expression
#if (412 + 42
     ~~~~~~~~^
t.c:5:5: error: to match this '('
#if (412 + 42
    ^
t.c:10:10: warning: left side of operator converted from negative value to unsigned: -42 to 18446744073709551574
#if (-42 + 0U) / -2
     ~~~ ^ ~~
t.c:10:16: warning: right side of operator converted from negative value to unsigned: -2 to 18446744073709551614
#if (-42 + 0U) / -2
    ~~~~~~~~~~ ^ ~~
5 diagnostics generated.

llvm-svn: 50638