[AST] Use PrintingPolicy for format string diagnosis

[jrtc27]

Summary

This is a small improvement for OpenCL diagnostics, but is also useful
for our CHERI fork, as our __capability qualifier is suppressed from
diagnostics when all pointers are capabilities, only being used when pointers
need to be explicitly opted-in to being capabilities.

[aaron.ballman]

LGTM!

[Anastasia]

LGTM! Thanks!

clang/lib/AST/FormatString.cpp

QualType ArgType::getRepresentativeType(ASTContext &C) const {
   }
 
   if (Ptr)
     Res = C.getPointerType(Res);
   return Res;
 }
 
 std::string ArgType::getRepresentativeTypeName(ASTContext &C) const {
-  std::string S = getRepresentativeType(C).getAsString();
+  std::string S = getRepresentativeType(C).getAsString(C.getPrintingPolicy());
 
   std::string Alias;
   if (Name) {
     // Use a specific name for this type, e.g. "size_t".
     Alias = Name;
     if (Ptr) {
       // If ArgType is actually a pointer to T, append an asterisk.
       Alias += (Alias[Alias.size()-1] == '*') ? "*" : " *";

clang/test/SemaOpenCL/printf-format-strings.cl

kernel void format_v4f64(half4 arg_h, float4 arg_f, double4 arg_d)
 
   printf("%v4lA", arg_d);
   printf("%v4lA", arg_f); // expected-warning{{format specifies type 'double __attribute__((ext_vector_type(4)))' but the argument has type 'float4' (vector of 4 'float' values)}}
   printf("%v4lA", arg_h); // expected-warning{{format specifies type 'double __attribute__((ext_vector_type(4)))' but the argument has type 'half4' (vector of 4 'half' values)}}
 }
 
 kernel void format_v4f16(half4 arg_h, float4 arg_f, double4 arg_d)
 {
-  printf("%v4hf\n", arg_d); // expected-warning{{format specifies type '__fp16 __attribute__((ext_vector_type(4)))' but the argument has type 'double4' (vector of 4 'double' values)}}
-  printf("%v4hf\n", arg_f); // expected-warning{{format specifies type '__fp16 __attribute__((ext_vector_type(4)))' but the argument has type 'float4' (vector of 4 'float' values)}}
+  printf("%v4hf\n", arg_d); // expected-warning{{format specifies type 'half __attribute__((ext_vector_type(4)))' but the argument has type 'double4' (vector of 4 'double' values)}}
+  printf("%v4hf\n", arg_f); // expected-warning{{format specifies type 'half __attribute__((ext_vector_type(4)))' but the argument has type 'float4' (vector of 4 'float' values)}}
   printf("%v4hf\n", arg_h);
 }
 
 kernel void no_length_modifier_scalar_fp(float f) {
   printf("%hf", f); // expected-warning{{length modifier 'h' results in undefined behavior or no effect with 'f' conversion specifier}}
   printf("%hlf", f); // expected-warning{{length modifier 'hl' results in undefined behavior or no effect with 'f' conversion specifier}}
   printf("%lf", f); // expected-warning{{length modifier 'l' results in undefined behavior or no effect with 'f' conversion specifier}}
 }