Make quickfix dir change conditional on makeprg

Issue #370

Author: da-x

autoload/cargo/quickfix.vim

@@ -1,5 +1,6 @@
 function! cargo#quickfix#CmdPre() abort
-    if &filetype ==# 'rust' && get(b:, 'current_compiler', '') ==# 'cargo'
+    if &filetype ==# 'rust' && get(b:, 'current_compiler', '') ==# 'cargo' &&
+         \ &makeprg =~ '\V\^cargo\ \.\*'
         " Preserve the current directory, and 'lcd' to the nearest Cargo file.
         let b:rust_compiler_cargo_qf_has_lcd = haslocaldir()
         let b:rust_compiler_cargo_qf_prev_cd = getcwd()