linux: update header used for major macro

Newer versions of glibc indicate that they intend to move the major
macro from sys/types.h to sys/sysmacros.h. Add a check for the header
and include that earlier to ensure that the macro is provided by the
newer header when available/possible. This avoids an unnecessary warning
from the system headers.

Because `config_ac.h` is not available at the right location, we cannot
include the header to check whether the header is available.  Rely on
the compiler provided `__has_include` instead of the configure check.
Adjust the inclusion of `sys/cdefs.h` accordingly.

Author: compnerd

CMakeLists.txt

@@ -156,7 +156,6 @@ check_include_files("stdint.h" HAVE_STDINT_H)
 check_include_files("stdlib.h" HAVE_STDLIB_H)
 check_include_files("string.h" HAVE_STRING_H)
 check_include_files("strings.h" HAVE_STRINGS_H)
-check_include_files("sys/cdefs.h" HAVE_SYS_CDEFS_H)
 check_include_files("sys/guarded.h" HAVE_SYS_GUARDED_H)
 check_include_files("sys/stat.h" HAVE_SYS_STAT_H)
 check_include_files("sys/types.h" HAVE_SYS_TYPES_H)

cmake/config.h.in

@@ -176,9 +176,6 @@
 /* Define to 1 if you have the `sysconf' function. */
 #cmakedefine01 HAVE_SYSCONF
 
-/* Define to 1 if you have the <sys/cdefs.h> header file. */
-#cmakedefine01 HAVE_SYS_CDEFS_H
-
 /* Define to 1 if you have the <sys/guarded.h> header file. */
 #cmakedefine HAVE_SYS_GUARDED_H
 

os/linux_base.h

@@ -13,9 +13,12 @@
 #ifndef __OS_LINUX_BASE__
 #define __OS_LINUX_BASE__
 
+#if __has_include(<sys/sysmacros.h>)
+#include <sys/sysmacros.h>
+#endif
 #include <sys/param.h>
 
-#if HAVE_SYS_CDEFS_H
+#if __has_include(<sys/cdefs.h>)
 #include <sys/cdefs.h>
 #endif
 

private/private.h

@@ -39,7 +39,7 @@
 #if HAVE_UNISTD_H
 #include <unistd.h>
 #endif
-#if HAVE_SYS_CDEFS_H
+#if __has_include(<sys/cdefs.h>)
 #include <sys/cdefs.h>
 #endif
 #include <pthread.h>