Let ob-C and ob-fortran work correctly on Windows/Cygwin

* lisp/ob.el (org-babel-exeext): New defconst to hold extension for
  executables or nil if none.  Should be ".exe" for both Windows and
  Cygwin.

* lisp/ob-C.el (org-babel-C-execute): Use org-babel-exeext when
  constructing the target file name for the compiled executable.

* lisp/ob-fortran.el (org-babel-execute:fortran): Add org-babel-exeext
  when constructing the target file name for the compiled executable.

lisp/ob-C.el

@@ -88,9 +88,7 @@ or `org-babel-execute:C++'."
 			(cond
 			 ((equal org-babel-c-variant 'c) ".c")
 			 ((equal org-babel-c-variant 'cpp) ".cpp"))))
-         (tmp-bin-file (org-babel-temp-file
-			"C-bin-"
-			(if (equal system-type 'windows-nt) ".exe" "")))
+         (tmp-bin-file (org-babel-temp-file "C-bin-" org-babel-exeext))
          (cmdline (cdr (assoc :cmdline params)))
          (flags (cdr (assoc :flags params)))
          (full-body (org-babel-C-expand body params))

lisp/ob-fortran.el

@@ -46,7 +46,7 @@
 (defun org-babel-execute:fortran (body params)
   "This function should only be called by `org-babel-execute:fortran'"
   (let* ((tmp-src-file (org-babel-temp-file "fortran-src-" ".F90"))
-         (tmp-bin-file (org-babel-temp-file "fortran-bin-"))
+         (tmp-bin-file (org-babel-temp-file "fortran-bin-" org-babel-exeext))
          (cmdline (cdr (assoc :cmdline params)))
          (flags (cdr (assoc :flags params)))
          (full-body (org-babel-expand-body:fortran body params))

lisp/ob.el

@@ -28,6 +28,10 @@
 (require 'ob-eval)
 (require 'org-macs)
 
+(defconst org-babel-exeext
+  (if (memq system-type '(windows-nt cygwin))
+      ".exe"
+    nil))
 (defvar org-babel-call-process-region-original)
 (defvar org-src-lang-modes)
 (defvar org-babel-library-of-babel)