bug#70716: flymake-cc creates `-.o` files

["Mattias Engdegård" <mattias.engdegard@gmail.com>]

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`flymake-cc-use-special-make-target`, the standard value for `flymake-cc-command`, generates a command like

  make check-syntax CHK_SOURCES="-x c -c -"

which causes the compiler (at least Clang) to create the file `-.o` that is never cleaned up and whose name is mysterious and awkward to remove.

What about the patch below?


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diff --git a/lisp/progmodes/flymake-cc.el b/lisp/progmodes/flymake-cc.el
index 60e7da5d617..01f463454e9 100644
--- a/lisp/progmodes/flymake-cc.el
+++ b/lisp/progmodes/flymake-cc.el
@@ -95,9 +95,10 @@ flymake-cc-use-special-make-target
   (unless (executable-find "make") (error "Make not found"))
   `("make"
     "check-syntax"
-    ,(format "CHK_SOURCES=-x %s -c -"
+    ,(format "CHK_SOURCES=-x %s -c - -o %s"
              (cond ((derived-mode-p 'c++-mode) "c++")
-                   (t "c")))))
+                   (t "c"))
+             null-device)))
 
 (defvar-local flymake-cc--proc nil "Internal variable for `flymake-cc'.")