Shorten compilation times

Now fish shell stores version is a small file called by other files.
This means that a slight change which modifies one file won't cause
many of files to recompile.

The compilation unit is intentionally small, this is by design. The
smaller it is, the faster it will recompile, and it will be compiled
a lot.

fish.cpp

@@ -62,6 +62,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 #include "history.h"
 #include "path.h"
 #include "input.h"
+#include "fish_version.h"
 
 /* PATH_MAX may not exist */
 #ifndef PATH_MAX
@@ -360,7 +361,7 @@ static int fish_parse_opt(int argc, char **argv, std::vector<std::string> *out_c
                 fwprintf(stderr,
                          _(L"%s, version %s\n"),
                          PACKAGE_NAME,
-                         FISH_BUILD_VERSION);
+                         get_fish_version());
                 exit_without_destructors(0);
             }