[analyzer] INT50-CPP. Do not cast to an out-of-range enumeration checker

This checker implements a solution to the "INT50-CPP. Do not cast to an
out-of-range enumeration value" rule [1].
It lands in alpha for now, and a number of followup patches are planned in order
to enable it by default.

[1] https://www.securecoding.cert.org/confluence/display/cplusplus/INT50-CPP.+Do+not+cast+to+an+out-of-range+enumeration+value

Patch by: Endre Fülöp and Alexander Zaitsev!

Differential Revision: https://reviews.llvm.org/D33672

llvm-svn: 347513