fix compilation with glibc 2.26, major/minor functions, fixed #2

compilation error was:
  linux_sigar.c:1156:22: error: called object ‘major’ is not a function or function pointer
  linux_sigar.c:1157:22: error: called object ‘minor’ is not a function or function pointer

bindings/ruby/extconf.rb

@@ -49,6 +49,9 @@ when /mswin|mingw|cygwin|bccwin/
   have_library("version")
 when /linux/
   os = 'linux'
+  if have_header("sys/sysmacros.h")
+    $CPPFLAGS += ' -DLINUX_SYSMACROS'
+  end
 when /solaris|sun/
   os = 'solaris'
   have_library("nsl")

src/os/linux/linux_sigar.c

@@ -30,6 +30,10 @@
 #include "sigar_util.h"
 #include "sigar_os.h"
 
+#ifdef LINUX_SYSMACROS // added by extconf.rb
+    #include <sys/sysmacros.h>
+#endif
+
 #define pageshift(x) ((x) << sigar->pagesize)
 
 #define PROC_MEMINFO PROC_FS_ROOT "meminfo"