Fix warnings in LLDBWrapPython.cpp with gcc 4.9.

Summary:
I see a lot of following warnings in LLDBWrapPython.cpp while building with gcc 4.9 on Linux.
"warning: cast from type ‘const char*’ to type ‘char*’ casts away qualifiers [-Wcast-qual]"

Is it ok to add -Wno-cast-qual for this file in cmake for gcc. This option seems to be already present
for autotool case.

Reviewers: zturner, clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D13719

llvm-svn: 250380