pass the reason for failure up from MemoryBuffer and report it
in diagnostics when we fail to open a file.  This allows us to
report things like:

$ clang test.c -I.
test.c:2:10: fatal error: error opening file './foo.h': Permission denied
#include "foo.h"
         ^



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@90276 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed