[llvm-symbolizer] Fix parsing DW_AT_ranges in Fission skeleton compile unit DIEs.

Turns out that DW_AT_ranges_base attribute sets the offset for
DW_AT_ranges values specified in the .dwo file, but not for DW_AT_ranges specified
in the skeleton compile unit DIE in the main executable. This is extremely confusing,
and would hopefully be fixed in DWARF-5 when it's finalized. For now this
behavior makes sense, as otherwise Fission would break DWARF consumers who
doesn't know anything about DW_AT_ranges_base.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210809 91177308-0d34-0410-b5e6-96231b3b80d8

test/DebugInfo/Inputs/fission-ranges.cc

@@ -0,0 +1,17 @@
+static inline int inlined_f() {
+  volatile int x = 2;
+  return x;
+}
+
+int main() {
+  return inlined_f();
+}
+
+// Build instructions:
+// $ mkdir /tmp/dbginfo
+// $ cp fission-ranges.cc /tmp/dbginfo/
+// $ cd /tmp/dbginfo
+// $ gcc -gsplit-dwarf -O2 -fPIC fission-ranges.cc -c -o obj2.o
+// $ clang -gsplit-dwarf -O2 -fsanitize=address -fPIC -Dmain=foo fission-ranges.cc -c -o obj1.o
+// $ gcc obj1.o obj2.o -shared -o <output>
+// $ objcopy --remove-section=.debug_aranges <output>