[AST][Sema] Support unsigned __intcap in getCorrespondingSignedType

This is used by the new __make_signed(T) builtin. Note (signed) __intcap
is already handled by getCorrespondingUnsignedSignedType from many years
ago.

Fixes: 1a54ef1 ("[clang] adds unary type transformations as compiler built-ins")

Author: jrtc27

clang/lib/AST/ASTContext.cpp

@@ -12457,6 +12457,8 @@ QualType ASTContext::getCorrespondingSignedType(QualType T) const {
     return LongTy;
   case BuiltinType::ULongLong:
     return LongLongTy;
+  case BuiltinType::UIntCap:
+    return IntCapTy;
   case BuiltinType::UInt128:
     return Int128Ty;
   // wchar_t is special. It is either unsigned or not, but when it's unsigned,

clang/test/SemaCXX/cheri/intcap-make-signed-unsigned.cpp

@@ -0,0 +1,11 @@
+// RUN: %cheri_cc1 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+_Static_assert(__is_same(__make_signed(__intcap), __intcap), "");
+_Static_assert(__is_same(__make_signed(signed __intcap), __intcap), "");
+_Static_assert(__is_same(__make_signed(unsigned __intcap), __intcap), "");
+
+_Static_assert(__is_same(__make_unsigned(__intcap), unsigned __intcap), "");
+_Static_assert(__is_same(__make_unsigned(signed __intcap), unsigned __intcap), "");
+_Static_assert(__is_same(__make_unsigned(unsigned __intcap), unsigned __intcap), "");