Don't cause ICEs when auto profile file is not found with checking

Don't cause ICEs when auto profile file is not found with checking

Currently, on a checking enabled compiler when -fauto-profile does
not find the profile feedback file it errors out with assertation
failures. Add proper errors for this case.

gcc/:

2016-05-30  Andi Kleen  <ak@linux.intel.com>

	* auto-profile.c (read_profile): Replace asserts with errors
	when file does not exist.
	* gcov-io.c (gcov_read_words): Dito.

From-SVN: r236894