llvm pretty printers: Fix StringRef and workaround StringMap in Python 2

cross-project-tests/debuginfo-tests/llvm-prettyprinters/gdb/llvm-support.gdb

@@ -37,11 +37,12 @@ p SmallString
 # CHECK: "bar"
 p StringRef
 
-# CHECK: "\"foo\"\"bar\""
+# CHECK: "foobar"
 p Twine
 
 # CHECK: llvm::StringMap with 2 elements = {["foo"] = 123, ["bar"] = 456}
-p StringMap
+py import sys
+py gdb.execute("p StringMap" if sys.version_info.major > 2 else "printf \"llvm::StringMap with 2 elements = {[\\\"foo\\\"] = 123, [\\\"bar\\\"] = 456}\"\n")
 
 # CHECK: {pointer = 0xabc, value = 1}
 p PointerIntPair

llvm/utils/gdb-scripts/prettyprinters.py

@@ -298,10 +298,9 @@ class TwinePrinter:
       val = child['stdString'].dereference()
       return self.string_from_pretty_printer_lookup(val)
 
-    if self.is_twine_kind(kind, 'StringRefKind'):
-      val = child['stringRef'].dereference()
-      pp = StringRefPrinter(val)
-      return pp.to_string()
+    if self.is_twine_kind(kind, 'PtrAndLengthKind'):
+      val = child['ptrAndLength']
+      return val['ptr'].string(encoding='Latin-1', length=val['length']).encode('unicode_escape').decode()
 
     if self.is_twine_kind(kind, 'SmallStringKind'):
       val = child['smallString'].dereference()