Don't remove PIE executables when using svr4 packets

Summary:
Because PIE executables have an e_type of llvm::ELF::ET_DYN,
they are not of type eTypeExecutable, and were being removed
when svr4 packets were used.

Reviewers: clayborg, ADodds, tfiala, sas

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D20990

llvm-svn: 271899