[build] try to silence some warnings

src/hist_source.hh

@@ -345,7 +345,7 @@ public:
 
         lc.get_dimensions(height, width);
 
-        for (int lpc = 0; lpc < this->sbc_idents.size(); lpc++) {
+        for (size_t lpc = 0; lpc < this->sbc_idents.size(); lpc++) {
             if (this->sbc_ident_to_show == -1 || lpc == this->sbc_ident_to_show) {
                 overall_stats.merge(this->sbc_idents[lpc].ci_stats, this->sbc_do_stacking);
             }

src/shlex.hh

@@ -345,7 +345,7 @@ public:
     };
 
     const char *s_str;
-    size_t s_len;
+    ssize_t s_len;
     size_t s_index;
     state_t s_state;
 };

src/yajlpp.hh

@@ -588,7 +588,7 @@ public:
                     "error: Invalid configuration option -- %s (%s)\n",
                     path.c_str(),
                     jph->jph_description);
-            for (int lpc = 0; lpc < error_list.size(); lpc++) {
+            for (size_t lpc = 0; lpc < error_list.size(); lpc++) {
                 fprintf(out, "error:   %s\n", error_list[lpc].c_str());
             }
             fprintf(out, "error: Use the following lnav command to fix the configuration:\n");