[sledge] Make workaround for broken llvm-config easier

Summary:
Change the Makefile comment about how to enable shared library linking
despite llvm-config being broken into a rule.

Reviewed By: ngorogiannis

Differential Revision: D28907814

fbshipit-source-id: ac63d0104

sledge/Makefile

@@ -27,13 +27,14 @@ LLVM_OCAML_SRC = $(shell git ls-files -- vendor/llvm-dune)
 # file to use as a sentinel indicating llvm ocaml bindings are up-to-date
 LLVM_OCAML_SENTINEL=vendor/llvm-dune/src/llvm/common/dune
 
-# Note that this does not correctly detect llvm shared libraries on
-# macos since llvm-config is broken. A filthy workaround seems to be
-# to create the libLLVM-11.dylib file llvm-config looks for as a
-# symbolic link to libLLVM.dylib. That is, to manually in the shell
-# execute:
-# (LLVMLIB=$($(opam config var conf-llvm:config) --libdir);
-#  ln -s $LLVMLIB/libLLVM.dylib $LLVMLIB/libLLVM-11.dylib)
+# Note that llvm-config is broken and does not correctly detect llvm
+# shared libraries. A filthy workaround seems to be to create the
+# libLLVM-11.dylib file llvm-config looks for as a symbolic link to
+# libLLVM.dylib.
+link_llvm_dylib:
+	@set -e ;\
+	LLVMLIB=$$($$(opam config var conf-llvm:config) --libdir) ;\
+	ln -s $$LLVMLIB/libLLVM.dylib $$LLVMLIB/libLLVM-11.dylib
 
 $(LLVM_OCAML_SENTINEL): $(LLVM_OCAML_SRC)
 	cd vendor/llvm-dune; ./setup.sh $$(opam config var conf-llvm:config) &>/dev/null