[PDB] Restore the calling convention from PDB

Summary:
This patch implements restoring of the calling convention from PDB.
It is necessary for expressions evaluation, if we want to call a function
of the debuggee process with a calling convention other than ccall.

Reviewers: clayborg, zturner, labath, asmith

Reviewed By: clayborg

Subscribers: teemperor, lldb-commits, stella.stamenova

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D52501

llvm-svn: 343084