Makefile.build: follow-up of commits by Matej on VERBOSE and READABLE_ML4

 - With the ?= construction, we avoid warnings about undefined variables,
   while tolerating both 'make VERBOSE=1' and 'VERBOSE=1 make'

 - Some extra documentation and cleanup

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 34ce67b7d..6649542c8 100644
--- a/Makefile
+++ b/Makefile
@@ -118,7 +118,7 @@ help:
 	@echo
 	@echo "For make to be verbose, add VERBOSE=1"
 	@echo
-	@echo "If you want camlp{4,5} to generate human-readable files, add NO_RECOMPILE_ML4=1"
+	@echo "If you want camlp{4,5} to generate human-readable files, add READABLE_ML4=1"
 
 UNSAVED_FILES:=$(shell find . -name '.\#*v' -o -name '.\#*.ml' -o -name '.\#*.ml?')
 ifdef UNSAVED_FILES