fix shell script

BUILD/check-cpu:
  make comparison a little more compatible with less exotic shells

BUILD/check-cpu

@@ -160,13 +160,18 @@ check_cpu () {
 
   cc_ver=`$cc --version | sed 1q`
   cc_verno=`echo $cc_ver | sed -e 's/^.*gcc/gcc/g; s/[^0-9. ]//g;	 s/^ *//g; s/ .*//g'`
+  set -- `echo $cc_verno | tr '.' ' '`
+  cc_major=$1
+  cc_minor=$2
+  cc_patch=$3
+  cc_comp=`expr $cc_major '*' 100 '+' $cc_minor`
 
   case "$cc_ver--$cc_verno" in
     *GCC*)
         # different gcc backends (and versions) have different CPU flags
         case `gcc -dumpmachine` in
           i?86-*)
-	    if test "$cc_verno" -lt "3.4"
+	    if test "$cc_comp" -lt 304
             then
                             check_cpu_args='-mcpu=$cpu_arg'
             else
@@ -177,7 +182,7 @@ check_cpu () {
                     check_cpu_args='-mcpu=$cpu_arg -mtune=$cpu_arg'
             ;;
           x86_64-*)
-	    if test "$cc_verno" -lt "3.4"
+	    if test "$cc_comp" -lt 304
             then
                             check_cpu_args='-mcpu=$cpu_arg'
             else