Get function start line number from DWARF info

DWARF info contains info about the line number at which a function starts (DW_AT_decl_line).

This patch creates a function to look up the start line number for a function, and returns it in
DILineInfo when looking up debug info for a particular address.

Patch by Simon Que!

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D27962

llvm-svn: 294231
diff --git a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
index aae009e..c1e2536 100644
--- a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
+++ b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
@@ -84,6 +84,8 @@
     return;
   }
   OS << "  Filename: " << Filename << "\n";
+  if (Info.StartLine)
+    OS << "Function start line: " << Info.StartLine << "\n";
   OS << "  Line: " << Info.Line << "\n";
   OS << "  Column: " << Info.Column << "\n";
   if (Info.Discriminator)