Use access(2) to determine if a file/directory exists

access(2) does not need to validate and fill in the buffer passed to the
kernel, so it's slightly faster.


Commit migrated from dotnet/core-setup@7d70bbe

src/installer/corehost/common/pal.unix.cpp

@@ -744,12 +744,7 @@ bool pal::realpath(pal::string_t* path, bool skip_error_logging)
 
 bool pal::file_exists(const pal::string_t& path)
 {
-    if (path.empty())
-    {
-        return false;
-    }
-    struct stat buffer;
-    return (::stat(path.c_str(), &buffer) == 0);
+    return (::access(path.c_str(), F_OK) == 0);
 }
 
 static void readdir(const pal::string_t& path, const pal::string_t& pattern, bool onlydirectories, std::vector<pal::string_t>* list)