Make build_check_stmt accept an SSA_NAME for its base

Make build_check_stmt accept an SSA_NAME for its base

This patch makes build_check_stmt accept its memory access parameter
to be an SSA name.  This is useful for a subsequent patch that will
re-use.

Tested by running cc1 -fasan on the program below with and without the
patch and inspecting the gimple output to see that there is no change.

void
foo ()
{
  char foo[1] = {0};

  foo[0] = 1;
}

gcc/
	* asan.c (build_check_stmt): Accept the memory access to be
	represented by an SSA_NAME.

From-SVN: r193438