DebugInfo: Add a driver flag for DWARF debug_ranges base address specifier use.

Summary:
This saves a lot of relocations in optimized object files (at the cost
of some cost/increase in linked executable bytes), but gold's 32 bit
gdb-index support has a bug (
https://sourceware.org/bugzilla/show_bug.cgi?id=21894 ) so we can't
switch to this unconditionally. (& even if it weren't for that bug, one
might argue that some users would want to optimize in one direction or
the other - prioritizing object size or linked executable size)

Differential Revision: https://reviews.llvm.org/D54243

llvm-svn: 346789
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 7be183f..32937d8 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -651,6 +651,7 @@
           : Args.hasArg(OPT_gpubnames)
                 ? llvm::DICompileUnit::DebugNameTableKind::Default
                 : llvm::DICompileUnit::DebugNameTableKind::None);
+  Opts.DebugRangesBaseAddress = Args.hasArg(OPT_fdebug_ranges_base_address);
 
   setPGOInstrumentor(Opts, Args, Diags);
   Opts.InstrProfileOutput =