[Hurd]: use /proc/self/exe to get program path

[kristina]

Is there a better way to check for a Hurd host than using the __GNU__ preprocessor macro? I'm worried it may cause some confusion otherwise similar to the issue with Hurd triples. It seems that Hurd target defines __gnu_hurd__, which is a lot less ambiguous and probably self-explanatory than __GNU__ (especially considering how often __GNUC__ is defined and given that it has a completely different meaning). Aside from that, LGTM!

[sthibaul]

gnu_hurd can work as well indeed

[kristina]

In D69683#1730353, @sthibaul wrote:

gnu_hurd can work as well indeed

LGTM! Let me know if you need this committed.

[sthibaul]

Here it is updated to use gnu_hurd, please commit indeed

llvm/lib/Support/Unix/Path.inc

if (len > 0) {
       len = std::min(len, ssize_t(sizeof(exe_path) - 1));
       exe_path[len] = '\0';
       return exe_path;
     }
   }
   // If we don't have procfs mounted, fall back to argv[0]
   if (getprogpath(exe_path, argv0) != NULL)
     return exe_path;
-#elif defined(__linux__) || defined(__CYGWIN__)
+#elif defined(__linux__) || defined(__CYGWIN__) || defined(__gnu_hurd__)
   char exe_path[MAXPATHLEN];
   const char *aPath = "/proc/self/exe";
   if (sys::fs::exists(aPath)) {
     // /proc is not always mounted under Linux (chroot for example).
     ssize_t len = readlink(aPath, exe_path, sizeof(exe_path));
     if (len < 0)
       return "";