Ensure IPFS-BUILD-OPTIONS build dependency is created

If the file doesn't exist, make will conclude that the missing
prerequisite should trigger a rebuild of the binaries.

test/bin/checkflags

@@ -14,9 +14,11 @@ shift
 shift
 FLAG_MSGS="$@"
 
+test -f $FLAG_FILE || touch $FLAG_FILE
+
 # Use x in front of tested values as flags could be
 # interpreted by "test" to be for itself.
-if test x"$FLAG_VALS" != x"$(cat "$FLAG_FILE" 2>/dev/null)"
+if test x"$FLAG_VALS" != x"$(cat "$FLAG_FILE")"
 then
     echo "$FLAG_MSGS"
     echo "$FLAG_VALS" >"$FLAG_FILE"