Define O_PATH if not already defined

linux/LinuxProcessList.c

@@ -57,6 +57,12 @@ in the source distribution for its full text.
 #endif
 
 
+// CentOS 6's kernel doesn't provide a definition of O_PATH
+// based on definition taken from uapi/asm-generic/fcnth.h in Linux kernel tree
+#ifndef O_PATH
+# define O_PATH 010000000
+#endif
+
 static FILE* fopenat(openat_arg_t openatArg, const char* pathname, const char* mode) {
    assert(String_eq(mode, "r")); /* only currently supported mode */