mksysinfo.sh: always define CLONE_NEWNET

CLONE_NEWNET is needed to compile the syscall tests on GNU/Linux.
    The symbol is not defined in the CentOS 5.11 header files.
    
    Patch from Uros Bizjak.
    
    Reviewed-on: https://go-review.googlesource.com/26630

From-SVN: r239296

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-58be5c6c7d92182dec50a62c8e319d2d7aab12a4
+d3636ca659ed7eed6d2e1cedfa0adccc6d81c07d
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/mksysinfo.sh

@@ -1475,6 +1475,9 @@ grep '^const _CLONE_' gen-sysinfo.go | \
 if ! grep '^const CLONE_NEWUSER ' ${OUT} > /dev/null 2>&1; then
   echo "const CLONE_NEWUSER = 0x10000000" >> ${OUT}
 fi
+if ! grep '^const CLONE_NEWNET ' ${OUT} > /dev/null 2>&1; then
+  echo "const CLONE_NEWNET = 0x40000000" >> ${OUT}
+fi
 
 # Struct sizes.
 set cmsghdr Cmsghdr ip_mreq IPMreq ip_mreqn IPMreqn ipv6_mreq IPv6Mreq \