Use "_$" prefix instead of "$" for dynamic checker function inserted by LLDB...

Use "_$" prefix instead of "$" for dynamic checker function inserted by LLDB during expression evaluation
    
    SUMMARY:
    The symbol "$" has a special meaning for MIPS i.e it is marker for temporary symbols for MIPS.
    So this patch uses additional _ prefix for "$__lldb_valid_pointer_check" so that it wont be marked as temporary symbol in case of MIPS.
    
    Reviewers: clayborg, spyffe
    Subscribers: dean, emaste, mohit.bhakkad, sagar, jaydeep, lldb-commits
    Differential http://reviews.llvm.org/D14111

llvm-svn: 258485