Fixes for platforms that default to unsigned char

[uweigand]

Summary

This fixes several test case failure on s390x caused by the fact that
on this platform, the default "char" type is unsigned.

• In ClangASTContext::GetBuiltinTypeForEncodingAndBitSize we should return an explicit *signed* char type for encoding eEncodingSint and bit size 8, instead of the default platform char type (which may be unsigned). This fix matches existing code in ClangASTContext::GetIntTypeFromBitSize, and fixes the TestClangASTContext.TestBuiltinTypeForEncodingAndBitSize unit test case.

• The test/expression_command/char/TestExprsChar.py test case is known to fail on platforms defaulting to unsigned char (pr23069), and just needs to be xfailed on s390x like on arm.

• The test/functionalities/watchpoint/watchpoint_on_vectors/main.c test case defines a vector of "char" and implicitly assumes to be signed. Use an explicit "signed char" instead.

[clayborg]

Looks good.

packages/Python/lldbsuite/test/expression_command/char/TestExprsChar.py

def do_test(self, dictionary=None):
         self.assertTrue(value.IsValid())
         self.assertTrue(value.GetError().Success())
         self.assertEqual(value.GetValueAsSigned(0), 3)
 
     @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr21765")
     def test_default_char(self):
         self.do_test()
 
-    @expectedFailureAll(archs=["arm", "aarch64"], bugnumber="llvm.org/pr23069")
+    @expectedFailureAll(archs=["arm", "aarch64", "s390x"], bugnumber="llvm.org/pr23069")
     @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr21765")
     def test_signed_char(self):
         self.do_test(dictionary={'CFLAGS_EXTRAS': '-fsigned-char'})
 
     @expectedFailureAll(archs=["i[3-6]86", "x86_64"], bugnumber="llvm.org/pr23069")
     @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr21765")
     @expectedFailureAll(triple = 'mips*', bugnumber="llvm.org/pr23069")
     def test_unsigned_char(self):
         self.do_test(dictionary={'CFLAGS_EXTRAS': '-funsigned-char'})

packages/Python/lldbsuite/test/functionalities/watchpoint/watchpoint_on_vectors/main.c

 //===-- main.c --------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-typedef char v4i8 __attribute__ ((vector_size(4)));
+typedef signed char v4i8 __attribute__ ((vector_size(4)));
 v4i8 global_vector = {1, 2, 3, 4};
 
 int
 main ()
 {
   return 0;
 }

source/Symbol/ClangASTContext.cpp

case eEncodingUint:
             return CompilerType (ast, ast->UnsignedLongTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->UnsignedLongLongTy))
             return CompilerType (ast, ast->UnsignedLongLongTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->UnsignedInt128Ty))
             return CompilerType (ast, ast->UnsignedInt128Ty);
         break;
         
     case eEncodingSint:
-        if (QualTypeMatchesBitSize (bit_size, ast, ast->CharTy))
-            return CompilerType (ast, ast->CharTy);
+        if (QualTypeMatchesBitSize (bit_size, ast, ast->SignedCharTy))
+            return CompilerType (ast, ast->SignedCharTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->ShortTy))
             return CompilerType (ast, ast->ShortTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->IntTy))
             return CompilerType (ast, ast->IntTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->LongTy))
             return CompilerType (ast, ast->LongTy);
         if (QualTypeMatchesBitSize (bit_size, ast, ast->LongLongTy))
             return CompilerType (ast, ast->LongLongTy);