[clang] Ensure proper NULL macro definition for system include files. (PR #149176)

[Eli Friedman via cfe-commits]

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+// There are at least 2 valid C null-pointer constants as defined
+// by the C language standard.
+// Test that the macro NULL is defined consistently for all platforms by
+// those headers that the C standard mandates a macro definition for NULL.
+
+// RUN: %clang %s -Dheader="<locale.h>" -E | tail -1 | FileCheck %s
+// RUN: %clang %s -Dheader="<stdio.h>" -E | tail -1 | FileCheck %s
+// RUN: %clang %s -Dheader="<stdlib.h>" -E | tail -1 | FileCheck %s
+// RUN: %clang %s -Dheader="<string.h>" -E | tail -1 | FileCheck %s
+// RUN: %clang %s -Dheader="<time.h>" -E | tail -1 | FileCheck %s
+// RUN: %clang %s -Dheader="<wchar.h>" -E | tail -1 | FileCheck %s
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efriedma-quic wrote:

The statement "Clang assumes the host triple" is an approximation.  clang's default target is specified by the LLVM_DEFAULT_TARGET_TRIPLE CMake flag.  By default, that's the host triple, but you can override it.

If you need some specific set of "libc" headers, you can mock them in clang/test/Headers/Inputs/ .

https://github.com/llvm/llvm-project/pull/149176