made -Wdocumentation a clang only flag
diff --git a/Makefile b/Makefile
index a6b2fb4..b7e0649 100644
--- a/Makefile
+++ b/Makefile
@@ -100,7 +100,7 @@
 
 clangtest: clean
 	clang -v
-	$(MAKE) all CC=clang MOREFLAGS="-Werror -Wconversion -Wno-sign-conversion"
+	$(MAKE) all CC=clang MOREFLAGS="-Werror -Wconversion -Wno-sign-conversion -Wdocumentation"
 
 armtest: clean
 	$(MAKE) -C $(TESTDIR) datagen   # use native, faster
diff --git a/lib/Makefile b/lib/Makefile
index 2836c95..579a906 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -49,7 +49,7 @@
 CPPFLAGS= -I. -I./common
 CFLAGS ?= -O3
 CFLAGS += -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow -Wstrict-aliasing=1 \
-          -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wundef -Wdocumentation
+          -Wswitch-enum -Wdeclaration-after-statement -Wstrict-prototypes -Wundef
 FLAGS   = $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(MOREFLAGS)