[analyzer] Strip trailing whitespace characters from input.

More universal way of removing trailing whitespace characters then 'chomp' does. Chomp "removes any trailing string that corresponds to the current value of $/" (quote from perldoc). In my case an input ended with '\r\r\n', chomp left '\r' at the end of input and the script ended up with an error "Use of uninitialized value in concatenation (.) or string"

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199892 91177308-0d34-0410-b5e6-96231b3b80d8