add FIXME

Author: Oneirical

tests/run-make/cat-and-grep-sanity-check/Makefile

@@ -1,6 +1,6 @@
 # grep in run-make tests was partially replaced with a custom script, CGREP. This tests that CGREP does its job correctly.
 # See https://github.com/rust-lang/rust/commit/ab788a2ee175c7560f0ca58bbc183ecfd57d2f7a
-# Note that this test will likely become useless after the port to rmake.rs tests (see https://github.com/rust-lang/rust/issues/121876)
+# FIXME(Oneirical): Note that this test will likely become useless after the port to rmake.rs tests (see https://github.com/rust-lang/rust/issues/121876)
 
 include ../tools.mk