[flang] Fix assert on bad character kind

[tskeith]

Summary

When we report an error for a bad character kind, don't keep it in the
DeclTypeSpec. Otherwise there could be further problems. In this case,
ComputeOffsets() got an assertion error because we didn't recognize
CHARACTER(*,8) as needing a descriptor because of the bad kind.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47173

flang/lib/Semantics/resolve-names.cpp

 void DeclarationVisitor::Post(const parser::CharSelector::LengthAndKind &x) {
   charInfo_.kind = EvaluateSubscriptIntExpr(x.kind);
   std::optional<std::int64_t> intKind{ToInt64(charInfo_.kind)};
   if (intKind &&
       !evaluate::IsValidKindOfIntrinsicType(
           TypeCategory::Character, *intKind)) { // C715, C719
     Say(currStmtSource().value(),
         "KIND value (%jd) not valid for CHARACTER"_err_en_US, *intKind);
+    charInfo_.kind = std::nullopt; // prevent further errors
   }
   if (x.length) {
     charInfo_.length = GetParamValue(*x.length, common::TypeParamAttr::Len);
   }
 }
 void DeclarationVisitor::Post(const parser::CharLength &x) {
   if (const auto *length{std::get_if<std::uint64_t>(&x.u)}) {
     charInfo_.length = ParamValue{

flang/test/Semantics/kinds02.f90

 character(len=*), parameter :: cvar7 = 1_"abcd"
 character(len=*), parameter :: cvar8 = 2_"abcd"
 !ERROR: CHARACTER(KIND=3) is not a supported type
 character(len=*), parameter :: cvar9 = 3_"abcd"
 character(len=*), parameter :: cvar10 = 4_"abcd"
 !ERROR: CHARACTER(KIND=8) is not a supported type
 character(len=*), parameter :: cvar11 = 8_"abcd"
 end program
+
+subroutine s(a, b)
+  character(*,2) :: a
+  !ERROR: KIND value (8) not valid for CHARACTER
+  character(*,8) :: b
+end