breakpad: Add FUNC records to the symtab

This patch extends SymbolFileBreakpad::AddSymbols to include the symbols
from the FUNC records too. These symbols come from the debug info and
have a size associated with them, so they are given preference in case
there is a PUBLIC record for the same address.

To achieve this, I first pre-process the symbols into a temporary
DenseMap, and then insert the uniqued symbols into the module's symtab.

Reviewers: clayborg, lemo, zturner

Reviewed By: clayborg

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D56590

llvm-svn: 351781