Provide option to set pc of the file loaded in memory.

Summary: This commit adds an option to set PC to the entry point of the file loaded using "target module load" command. In D28804, Greg asked me to separate this part under a different option.

Reviewers: clayborg

Reviewed By: clayborg

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D28944

llvm-svn: 292989