[AMDGCNSPIRV][NFC] Match AMDGPU's __builtin_va_list type (llvm#152044)

AMDGCN flavoured SPIRV should math AMDGPU TI as much as possible, and
the va_list difference was spurious.

Author: AlexVlx

clang/lib/Basic/Targets/SPIR.h

@@ -438,6 +438,10 @@ class LLVM_LIBRARY_VISIBILITY SPIRV64AMDGCNTargetInfo final
 
   ArrayRef<const char *> getGCCRegNames() const override;
 
+  BuiltinVaListKind getBuiltinVaListKind() const override {
+    return TargetInfo::CharPtrBuiltinVaList;
+  }
+
   bool initFeatureMap(llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags,
                       StringRef,
                       const std::vector<std::string> &) const override;

clang/test/Sema/amdgcn-va-list-type.c

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 %s -triple amdgcn-amd-amdhsa -fsyntax-only -verify
+// RUN: %clang_cc1 %s -triple spirv64-amd-amdhsa -fsyntax-only -verify
+
+// expected-no-diagnostics
+
+typedef char* va_list;
+
+void foo(const char* f, ...) {
+    int r;
+    va_list args;
+    __builtin_va_start(args, f);
+    __builtin_va_end(args);
+}