make cluster usage string a constant array

Minor clarity change that makes it more obvious to readers and the compiler that
this string is a constant that can be inlined at its usage site.

diff --git a/cmd/gvmap/cluster.c b/cmd/gvmap/cluster.c
index d7613ad6b678f0393f6ee2190c70bb9f1f6524a7..903fd8f1aef23e9c0c4d4ace01afc254ca1cc891 100644 (file)
--- a/cmd/gvmap/cluster.c
+++ b/cmd/gvmap/cluster.c
@@ -47,7 +47,7 @@ typedef struct {
   int clustering_method;
 } opts_t;
 
-static char* usestr =
+static const char usestr[] =
 "    -C k - generate no more than k clusters (0)\n\
        0 : no limit\n\
     -c k - use clustering method k (0)\n\