[clang] Display error if _Fract fixed point literals overflow

[gousemoodhin]

Summary

Values of a fract type are between -1.0 and +1.0.

[ebevhan]

This needs a few tests.

Testing it myself also shows that

unsigned _Fract f = 1.0ur;

seems to get an error, which it shouldn't.

[gousemoodhin]

In D86677#2241232, @ebevhan wrote:

This needs a few tests.

Testing it myself also shows that

unsigned _Fract f = 1.0ur;

seems to get an error, which it shouldn't.

Update:
Compiler makes overflow decision inside function GetFixedPointValue() - LiteralSupport.cpp

Case unsigned _Fract f = 1.0ur;

At LiteralSupport.cpp (between line 1149 - 1198)
The "Val" is 65,536, it shouldn't.
It causes overflow.

Checking how to handle cases like

unsigned _Fract f = 1.0ur;
unsigned _Fract f = 1.01ur;

clang/lib/Sema/SemaExpr.cpp

if (Literal.isFixedPointLiteral()) {
 
     auto MaxVal = Context.getFixedPointMax(Ty).getValue();
     if (Literal.isFract && Val == MaxVal + 1 && !ValIsZero)
       // Clause 6.4.4 - The value of a constant shall be in the range of
       // representable values for its type, with exception for constants of a
       // fract type with a value of exactly 1; such a constant shall denote
       // the maximal value for the type.
       --Val;
-    else if (Val.ugt(MaxVal) || Overflowed)
+
+    if (Val.ugt(MaxVal) || Overflowed)
       Diag(Tok.getLocation(), diag::err_too_large_for_fixed_point);
 
     Res = FixedPointLiteral::CreateFromRawInt(Context, Val, Ty,
                                               Tok.getLocation(), scale);
   } else if (Literal.isFloatingLiteral()) {
     QualType Ty;
     if (Literal.isHalf){
       if (getOpenCLOptions().isEnabled("cl_khr_fp16"))