[analyzer] Handle C string default values for const char * arguments.

Previously, SValBuilder knew how to evaluate StringLiterals, but couldn't
handle an array-to-pointer decay for constant values. Additionally,
RegionStore was being too strict about loading from an array, refusing to
return a 'char' value from a 'const char' array. Both of these have been
fixed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186520 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed