Use zlib to uncompress debug sections in DWARF parser.

This makes llvm-dwarfdump and llvm-symbolizer understand
debug info sections compressed by ld.gold linker.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180088 91177308-0d34-0410-b5e6-96231b3b80d8

test/DebugInfo/Inputs/dwarfdump-test-zlib.cc

@@ -0,0 +1,24 @@
+class DummyClass {
+  int a_;
+ public:
+  DummyClass(int a) : a_(a) {}
+  int add(int b) {
+    return a_ + b;
+  }
+};
+
+int f(int a, int b) {
+  DummyClass c(a);
+  return c.add(b);
+}
+
+int main() {
+  return f(2, 3);
+}
+
+// Built with Clang 3.2 and ld.gold linker:
+// $ mkdir -p /tmp/dbginfo
+// $ cp dwarfdump-test-zlib.cc /tmp/dbginfo
+// $ cd /tmp/dbginfo
+// $ clang++ -g dwarfdump-test-zlib.cc -Wl,--compress-debug-sections=zlib \
+//   -o <output>