[IRInterpreter] Fix misevaluation of interpretation expressions with `urem`

[davide]

Summary

Scalar::MakeUnsigned was implemented incorrectly so it didn't really change the sign of the type (leaving signed types signed).
This showed up as a misevaluation when IR-interpreting urem but it's likely to arise in other contexts.

This commit fixes the definition, and adds a test to make sure this won't regress in future (hopefully).

Fixes rdar://problem/42038760 and LLVM PR38076

[davide]

Ack'ed by Jim offline.

lldb/packages/Python/lldbsuite/test/expression_command/rdar42038760/Makefile

+LEVEL = ../../make
+C_SOURCES := main.c
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/rdar42038760/TestScalarURem.py

+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(), None)

lldb/packages/Python/lldbsuite/test/expression_command/rdar42038760/main.c

+// Make sure we IR-interpret the expression correctly.
+
+typedef unsigned int uint32_t;
+struct S0 {
+  signed f2;
+};
+static g_463 = 0x1561983AL;
+void func_1(void)
+{
+  struct S0 l_19;
+  l_19.f2 = 419;
+  uint32_t l_4037 = 4294967295UL;
+  l_19.f2 = g_463; //%self.expect("expr ((l_4037 % (-(g_463))) | l_19.f2)", substrs=['(unsigned int) $0 = 358717883'])
+}
+int main()
+{
+  func_1();
+  return 0;
+}

lldb/source/Core/Scalar.cpp

 
 bool Scalar::MakeUnsigned() {
   bool success = false;
 
   switch (m_type) {
   case e_void:
     break;
   case e_sint:
+    m_type = e_uint;
     success = true;
     break;
   case e_uint:
-    m_type = e_uint;
     success = true;
     break;
   case e_slong:
+    m_type = e_ulong;
     success = true;
     break;
   case e_ulong:
-    m_type = e_ulong;
     success = true;
     break;
   case e_slonglong:
+    m_type = e_ulonglong;
     success = true;
     break;
   case e_ulonglong:
-    m_type = e_ulonglong;
     success = true;
     break;
   case e_sint128:
+    m_type = e_uint128;
     success = true;
     break;
   case e_uint128:
-    m_type = e_uint128;
     success = true;
     break;
   case e_sint256:
+    m_type = e_uint256;
     success = true;
     break;
   case e_uint256:
-    m_type = e_uint256;
     success = true;
     break;
   case e_float:
     success = true;
     break;
   case e_double:
     success = true;
     break;