integer: Update integer limits to comply with spec

The values for the char/short/integer/long minimums were declared with
their actual values, not the definitions from the CL spec (v1.1).  As
a result, (-2147483648) was actually being treated as a long by the
compiler, not an int, which caused issues when trying to add/subtract
that value from a vector.

Update the definitions to use the values declared by the spec, and also
add explicit casts for the char/short/int minimums so that the compiler
actually treats them as shorts/chars. Without those casts, they
actually end up stored as integers, and the compiler may end up storing
the INT_MIN as a long.

The compiler can sign extend the values if it needs to convert the
char->short, short->int, or int->long

v2: Add explicit cast for INT_MIN and fix some type-o's and wrapping
    in the commit message.

Reported-by: Moritz Pflanzer <moritz.pflanzer14@imperial.ac.uk>
CC: Moritz Pflanzer <moritz.pflanzer14@imperial.ac.uk>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Aaron Watry <awatry@gmail.com>
llvm-svn: 247661