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.

env.cpp

@@ -55,6 +55,7 @@
 #include "path.h"
 
 #include "complete.h"
+#include "fish_version.h"
 
 /** Command used to start fishd */
 #define FISHD_CMD L"fishd ^ /tmp/fishd.log.%s"
@@ -599,7 +600,7 @@ void env_init(const struct config_paths_t *paths /* or NULL */)
     /*
       Set up the version variables
     */
-    wcstring version = str2wcstring(FISH_BUILD_VERSION);
+    wcstring version = str2wcstring(get_fish_version());
     env_set(L"version", version.c_str(), ENV_GLOBAL);
     env_set(L"FISH_VERSION", version.c_str(), ENV_GLOBAL);