Bug 1270091 - Handle missing function names. r=dminor

If the symbols file doesn't give a function name, substitute
'unnamed_function'. A more complete fix would be to catch
all ValueError exceptions and continue sensibly, but this
addresses the immediate issue with the output from `rustc -g`.

MozReview-Commit-ID: 666ruvLlJ5t

tools/rb/fix_stack_using_bpsyms.py

@@ -43,7 +43,10 @@ class SymbolFile:
         # http://code.google.com/p/google-breakpad/wiki/SymbolFiles
         if line.startswith("FUNC "):
           # FUNC <address> <size> <stack_param_size> <name>
-          (junk, rva, size, ss, name) = line.split(None, 4)
+          bits = line.split(None, 4)
+          if len(bits) < 5:
+            bits.append('unnamed_function')
+          (junk, rva, size, ss, name) = bits
           rva = int(rva,16)
           funcs[rva] = name
           addrs.append(rva)