fenv: fix up stub file comment, drop symlinks from description

also slightly fixed up formatting

newlib/libm/fenv/fenv_stub.c

@@ -1,22 +1,22 @@
 /*
  * SPDX-License-Identifier: BSD-2-Clause
- * 
+ *
  * (c) Copyright 2019 Joel Sherrill <joel@rtems.org
  */
 
 /*
- * This file is intentionally empty. 
+ * This file is intentionally empty.
  *
- * Newlib's build infrastructure needs a machine specific fiel to override
- * the generic implementation in the library.  When a target
- * implementation of the fenv.h methods puts all methods in a single file
- * (e.g. fenv.c) or some as inline methods in its <sys/fenv.h>, it will need
- * to override the default implementation found in a file in this directory.
+ * Newlib's build infrastructure needs a machine specific file to override
+ * the generic implementation in the library.  When a target implementation
+ * of the fenv.h methods puts all methods in a single file (e.g. fenv.c) or
+ * some as inline methods in its <sys/fenv.h>, it will need to override the
+ * default implementation found in a file in this directory.
  *
  * For each file that the target's machine directory needs to override,
- * this file should be symbolically linked to that specific file name
- * in the target directory. For example, the target may use fe_dfl_env.c
- * from the default implementation but need to override all others.
+ * there should be a corresponding stub file in the target directory.
+ * To avoid copying this explanation far and wide, #including this
+ * fenv_stub.c from the stub files in encouraged.
  */
 
 /* deliberately empty */