[clang] Make sure EvalInfo pointer isn't null (llvm#155563)

It can be null, when called via CheckICE().
Accidentally introduced via llvm#119366

Fixes llvm#155507

(cherry picked from commit 60cdc3d)

Author: tbaederr

clang/lib/AST/ExprConstant.cpp

@@ -7909,8 +7909,9 @@ static bool checkBitCastConstexprEligibilityType(SourceLocation Loc,
       // so its layout is unspecified. For now, we'll simply treat these cases
       // as unsupported (this should only be possible with OpenCL bool vectors
       // whose element count isn't a multiple of the byte size).
-      Info->FFDiag(Loc, diag::note_constexpr_bit_cast_invalid_vector)
-          << QualType(VTy, 0) << EltSize << NElts << Ctx.getCharWidth();
+      if (Info)
+        Info->FFDiag(Loc, diag::note_constexpr_bit_cast_invalid_vector)
+            << QualType(VTy, 0) << EltSize << NElts << Ctx.getCharWidth();
       return false;
     }
 
@@ -7919,8 +7920,9 @@ static bool checkBitCastConstexprEligibilityType(SourceLocation Loc,
       // The layout for x86_fp80 vectors seems to be handled very inconsistently
       // by both clang and LLVM, so for now we won't allow bit_casts involving
       // it in a constexpr context.
-      Info->FFDiag(Loc, diag::note_constexpr_bit_cast_unsupported_type)
-          << EltTy;
+      if (Info)
+        Info->FFDiag(Loc, diag::note_constexpr_bit_cast_unsupported_type)
+            << EltTy;
       return false;
     }
   }

clang/test/Sema/constexpr.c

@@ -391,3 +391,10 @@ void ghissue109095() {
   _Static_assert(i == c[0]); // expected-error {{static assertion expression is not an integral constant expression}}\
                              // expected-note {{initializer of 'i' is not a constant expression}}
 }
+
+typedef bool __vbool2  __attribute__((ext_vector_type(2)));
+typedef short v2int16_t __attribute__((ext_vector_type(2)));
+
+bool issue155507(v2int16_t a, v2int16_t b) {
+    return __builtin_bit_cast(unsigned char, __builtin_convertvector(a == b, __vbool2)) == 0b11;
+}