Fix bug in expression display when determining if a pointer should be treated as a string

Summary:
Currently if the "first child" of the pointer is a char type then the pointer is displayed as a string. This test succeeds incorrectly when the pointer is to a structured type with a char type as its first field. Fix this by switching the test to retrieve the pointee type and checking that it is a char type.


Reviewers: abidh, ChuckR, ki.stfu

Subscribers: greggm, lldb-commits

Differential Revision: http://reviews.llvm.org/D11488

llvm-svn: 243619