Provide for MSVC config equivalents of recently added configure options. Remove

any hardcoding of those options. Along the way, reorder the expression used to
calculate RELSEG_SIZE to make it slightly clearer. For now wal_segsize is only
allowed to have a value of 1 on Windows - we can relax that when we get full
large file support in the backend.

configure

@@ -2638,7 +2638,8 @@ fi
 
 
 # this expression is set up to avoid unnecessary integer overflow
-RELSEG_SIZE=`expr '(' 1024 '*' ${segsize} / ${blocksize} ')' '*' 1024`
+# blocksize is already guaranteed to be a factor of 1024
+RELSEG_SIZE=`expr '(' 1024 / ${blocksize} ')' '*' ${segsize} '*' 1024`
 test $? -eq 0 || exit 1
 { echo "$as_me:$LINENO: result: ${segsize}GB" >&5
 echo "${ECHO_T}${segsize}GB" >&6; }