Fixing build issue on newer linux and alos issue with newer Ruby

Rakefile

@@ -51,15 +51,15 @@ end
 desc 'Build sigar extension'
 task :build do
   in_ext()
-  unless File.exists? "Makefile"
+  unless File.exist? "Makefile"
     unless system("ruby extconf.rb")
       STDERR.puts "Failed to configure"
-      break
+      next
     end
   end
   unless system(MAKE)
     STDERR.puts 'Failed to ' + MAKE
-    break
+    next
   end
 end
 
@@ -75,13 +75,13 @@ end
 desc 'Clean sigar extension'
 task :clean do
   in_ext()
-  system(MAKE + ' clean') if File.exists? "Makefile"
+  system(MAKE + ' clean') if File.exist? "Makefile"
 end
 
 desc 'Dist Clean sigar extension'
 task :distclean do
   in_ext()
-  system(MAKE + ' distclean') if File.exists? "Makefile"
+  system(MAKE + ' distclean') if File.exist? "Makefile"
 end
 
 desc 'Run sigar examples (test)'

src/sigar_util.c

@@ -30,6 +30,7 @@
 
 #include <dirent.h>
 #include <sys/stat.h>
+#include <sys/time.h>
 
 SIGAR_INLINE char *sigar_uitoa(char *buf, unsigned int n, int *len)
 {