[glibc/maskray/clang] Skip undefined va_arg_pack

[Fangrui Song <maskray@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a2f9788c5f729e09e0eeaf514e816c9bf3f06171

commit a2f9788c5f729e09e0eeaf514e816c9bf3f06171
Author: Stan Shebs <stanshebs@google.com>
Date:   Fri Jan 19 09:31:04 2018 -0800

    Skip undefined va_arg_pack

Diff:
---
 misc/sys/cdefs.h           | 5 +++++
 sysdeps/generic/ldsodefs.h | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 4dac9d264d..574a4f1e85 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -406,9 +406,14 @@
 /* GCC 4.3 and above allow passing all anonymous arguments of an
    __extern_always_inline function to some other vararg function.  */
 #if __GNUC_PREREQ (4,3)
+#if defined(__clang__)
+# define __va_arg_pack() __VA_ARGS__
+# define __va_arg_pack_len() 0
+#else
 # define __va_arg_pack() __builtin_va_arg_pack ()
 # define __va_arg_pack_len() __builtin_va_arg_pack_len ()
 #endif
+#endif
 
 /* It is possible to compile containing GCC extensions even if GCC is
    run in pedantic mode if the uses are carefully marked using the
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 9ec1511bb0..f3651ab649 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -808,7 +808,11 @@ _dl_dprintf (int fd, const char *fmt, ...)
 {
   /* Use local declaration to avoid includign <stdio.h>.  */
   extern int __dprintf(int fd, const char *format, ...) attribute_hidden;
+#if defined(__clang__)
+  __dprintf (fd, fmt);
+#else
   __dprintf (fd, fmt, __builtin_va_arg_pack ());
+#endif
 }
 #endif