netrw: Fix including {stdlib,stdio,string}.h

With GCC 14 it is no longer possible to call a function that has not
been declared and thus we get build errors like these:

  netread.c:69:5: error: implicit declaration of function 'fprintf'
  netread.c:89:5: error: implicit declaration of function 'exit'
  ../version.h:37:9: error: implicit declaration of function 'puts'

Instead of ignoring this error, I looked around in the netrw code and
found that there is a STDC_HEADERS preprocessor variable that makes sure
that those includes are explicit.

The configure script confusingly calls the check "ANSI C header files",
so I made sure that the STDC_HEADERS variable really only adds
"#include" directives.

Signed-off-by: aszlig <aszlig@nix.build>

pkgs/by-name/ne/netrw/package.nix

@@ -15,6 +15,9 @@ stdenv.mkDerivation rec {
   version = "1.3.2";
 
   configureFlags = [
+    # This is to add "#include" directives for stdlib.h, stdio.h and string.h.
+    "ac_cv_header_stdc=yes"
+
     "--with-checksum=${checksumType}"
   ];