This broke for example the 'not' utility, if a directory called
'FileCheck' is executable and in the path before the actual 'FileCheck'.
This patch steals the implementation of the "old" PathV1 canExecute
implementation:
- checks for R_OK (file readable): this is necessary for executing
scripts; we should not regress here unless we have good reasons
- checks for S_ISREG; if we want to get rid of this, we'd need to
change all callers who already made the assumption when depending
on Path V1.
llvm-svn: 184074
52772bf356