Summary:
When the code is compiled for arm32 and the builtin `__va_list` declaration is created by `CreateAAPCSABIBuiltinVaListDecl`, the declaration is not saved in the `ASTContext` which may lead to a compilation error or crash.
Minimal reproducer I was able to find:
**header.h**
```
#include <stdarg.h>
typedef va_list va_list_1;
```
**test.cpp**
```
typedef __builtin_va_list va_list_2;
void foo(const char* format, ...) { va_list args; va_start( args, format ); }
```
Steps to reproduce:
```
clang -x c++-header --target=armv7l-linux-eabihf header.h
clang -c -include header.h --target=armv7l-linux-eabihf test.cpp
```
Compilation error:
```
error: non-const lvalue reference to type '__builtin_va_list'
cannot bind to a value of unrelated type 'va_list' (aka '__builtin_va_list')
```
Compiling the same code as a C source leads to a crash:
```
clang --target=armv7l-linux-eabihf header.h
clang -c -x c -include header.h --target=armv7l-linux-eabihf test.cpp
```
Reviewers: logan, rsmith
Subscribers: cfe-commits, asl, aemerson, rengolin
Differential Revision: http://reviews.llvm.org/D18557
llvm-svn: 264930
// };
VaListDecl->completeDefinition();
+ Context->VaListTagDecl = VaListDecl;
// typedef struct __va_list __builtin_va_list;
QualType T = Context->getRecordType(VaListDecl);
--- /dev/null
+// Header for PCH test __va_list_tag-typedef.c
+
+#include <stdarg.h>
+typedef va_list va_list_1;
--- /dev/null
+// This test checks the patch for the compilation error / crash described in D18557.
+
+// Test as a C source
+// RUN: %clang_cc1 -emit-pch -x c-header -o %t %S/Inputs/__va_list_tag-typedef.h
+// RUN: %clang_cc1 -fsyntax-only -include-pch %t %s
+
+// Test as a C++ source
+// RUN: %clang_cc1 -emit-pch -x c++-header -o %t %S/Inputs/__va_list_tag-typedef.h
+// RUN: %clang_cc1 -x c++ -fsyntax-only -include-pch %t %s
+
+// expected-no-diagnostics
+
+typedef __builtin_va_list va_list_2;
+void test(const char* format, ...) { va_list args; va_start( args, format ); }