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.

mimedb.cpp

@@ -51,6 +51,7 @@ license. Read the source code of the library for more information.
 #include "fallback.h"
 #include "util.h"
 #include "print_help.h"
+#include "fish_version.h"
 
 typedef std::vector<std::string> string_list_t;
 
@@ -1332,7 +1333,7 @@ int main(int argc, char *argv[])
                 exit(0);
 
             case 'v':
-                printf(_("%s, version %s\n"), MIMEDB, FISH_BUILD_VERSION);
+                printf(_("%s, version %s\n"), MIMEDB, get_fish_version());
                 exit(0);
 
             case '?':