[PATCH v2] libc: Don't use a custom wrapper macro around __has_include.

[Emilio Cobos Álvarez <emilio at crisal dot io>]

This causes issues when using clang with -frewrite-includes to e.g., submit the
translation unit to a distributed compiler.

In my case, I was building Firefox using sccache.

See [1] for a reduced test-case since I initially thought this was a clang bug,
and [2] for more context.

Apparently doing this is invalid C++ per [cpp.cond], which mentions [3]:

> The #ifdef and #ifndef directives, and the defined conditional inclusion
> operator, shall treat __has_include and __has_cpp_attribute as if they
> were the names of defined macros.  The identifiers __has_include and
> __has_cpp_attribute shall not appear in any context not mentioned in this
> subclause.

[1]: https://bugs.llvm.org/show_bug.cgi?id=43982
[2]: https://bugs.llvm.org/show_bug.cgi?id=37990
[3]: http://eel.is/c++draft/cpp.cond#7.sentence-2
---
 misc/sys/cdefs.h                     |  8 --------
 sysdeps/unix/sysv/linux/bits/statx.h | 12 +++++++-----
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index abcb0d5e3c..467dbd9547 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -412,14 +412,6 @@
 # define __glibc_has_attribute(attr)	0
 #endif
 
-#ifdef __has_include
-/* Do not use a function-like macro, so that __has_include can inhibit
-   macro expansion.  */
-# define __glibc_has_include __has_include
-#else
-# define __glibc_has_include(header)	0
-#endif
-
 #if (!defined _Noreturn \
      && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
      &&  !__GNUC_PREREQ (4,7))
diff --git a/sysdeps/unix/sysv/linux/bits/statx.h b/sysdeps/unix/sysv/linux/bits/statx.h
index ff3f2e8973..2015c8262e 100644
--- a/sysdeps/unix/sysv/linux/bits/statx.h
+++ b/sysdeps/unix/sysv/linux/bits/statx.h
@@ -26,11 +26,13 @@
 
 /* Use "" to work around incorrect macro expansion of the
    __has_include argument (GCC PR 80005).  */
-#if __glibc_has_include ("linux/stat.h")
-# include "linux/stat.h"
-# ifdef STATX_TYPE
-#  define __statx_timestamp_defined 1
-#  define __statx_defined 1
+#ifdef __has_include
+# if __has_include ("linux/stat.h")
+#  include "linux/stat.h"
+#  ifdef STATX_TYPE
+#   define __statx_timestamp_defined 1
+#   define __statx_defined 1
+#  endif
 # endif
 #endif
 
-- 
2.24.0