Fix DwarfSymbolFile when appending global functions from different modules

[ADodds]

Summary

This patch fixes a bug in SymbolFileDWARF::FindFunctions(), where functions may not be correctly found when appending to a list already containing some symbols.
Upon entering this function, original_size is set to the size of sc_list, however the target code should be executed not when the list is empty but when this list has not grown during this function invocation. This patch corrects this problem.

Running the lldb test suite shows no regressions caused by this change, and fixes Bug 25433.
https://llvm.org/bugs/show_bug.cgi?id=25433

[tberghammer]

Looks good (I remember fixing some similar issues in SymbolFileDWARF where we specify append=true, but I missed this one)

lldb/trunk/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

else
             // functions debugging FreeBSD and Linux binaries.
             // If we didn't find any functions in the global namespace try
             // looking in the basename index but ignore any returned
             // functions that have a namespace but keep functions which
             // have an anonymous namespace
             // TODO: The arch in the object file isn't correct for MSVC
             // binaries on windows, we should find a way to make it
             // correct and handle those symbols as well.
-            if (sc_list.GetSize() == 0)
+            if (sc_list.GetSize() == original_size)
             {
                 ArchSpec arch;
                 if (!parent_decl_ctx &&
                     GetObjectFile()->GetArchitecture(arch) &&
                     (arch.GetTriple().isOSFreeBSD() || arch.GetTriple().isOSLinux() ||
                      arch.GetMachine() == llvm::Triple::hexagon))
                 {
                     SymbolContextList temp_sc_list;