SystemTools: move some code around that is used only on Windows-like platforms

The list of possible extensions is only filled inside an #ifdef, so the whole
usage of this list can be moved into that #ifdef's, too. The loop can be
completely avoided if it's already known that the list will not be filled at
all.

Change-Id: I89a87115babf68f9bf99d4ad523cb0851c252cd9

SystemTools.cxx

@@ -2970,6 +2970,8 @@ std::string SystemTools::FindProgram(
   bool no_system_path)
 {
   std::vector<std::string> extensions;
+  std::string tryPath;
+
 #if defined (_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__)
   bool hasExtension = false;
   // check to see if the name already has a .xxx at
@@ -2983,22 +2985,22 @@ std::string SystemTools::FindProgram(
     {
     extensions.push_back(".com");
     extensions.push_back(".exe");
-    }
-#endif
-  std::string tryPath;
 
-  // first try with extensions if the os supports them
-  for(std::vector<std::string>::iterator i =
-        extensions.begin(); i != extensions.end(); ++i)
-    {
-    tryPath = name;
-    tryPath += *i;
-    if(SystemTools::FileExists(tryPath) &&
-        !SystemTools::FileIsDirectory(tryPath))
+    // first try with extensions if the os supports them
+    for(std::vector<std::string>::iterator i =
+          extensions.begin(); i != extensions.end(); ++i)
       {
-      return SystemTools::CollapseFullPath(tryPath);
+      tryPath = name;
+      tryPath += *i;
+      if(SystemTools::FileExists(tryPath) &&
+          !SystemTools::FileIsDirectory(tryPath))
+        {
+        return SystemTools::CollapseFullPath(tryPath);
+        }
       }
     }
+#endif
+
   // now try just the name
   tryPath = name;
   if(SystemTools::FileExists(tryPath) &&