Revert r117582, which reverted r77396. Searching PATH for a string

which contains slashes is inconsistent with the meaning of PATH on
Unix-type platforms, and pretty surprising.

If the user has given a specific path to execute and we can't
execute it, we should fail and say why.  (Apparently the new
posix_spawn code doesn't always say why, but that's a separate
issue.)

llvm-svn: 117596

llvm/lib/System/Unix/Program.inc

@@ -63,7 +63,7 @@ Program::FindProgramByName(const std::string& progName) {
     return Path();
   // Use the given path verbatim if it contains any slashes; this matches
   // the behavior of sh(1) and friends.
-  if (progName.find('/') != std::string::npos && temp.canExecute())
+  if (progName.find('/') != std::string::npos)
     return temp;
 
   // At this point, the file name does not contain slashes. Search for it