Add build_type string to version.c

src/version.c.in

@@ -7,4 +7,5 @@ const int ucore_version_patch = @version_patch@;
 
 const char ucore_version_str[] = "@version_str@";
 const char ucore_build_host[] = "@build_host@";
+const char ucore_build_type[] = "@build_type@";