Build the docs directory last

Ensure that other components are built before generating the
documentation.

v2: build the docs directory after any optional directories

Signed-off-by: Thomas Wood <thomas.wood@intel.com>
diff --git a/Makefile.am b/Makefile.am
index 1dacb17..4f71a3a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -21,7 +21,7 @@
 
 ACLOCAL_AMFLAGS = ${ACLOCAL_FLAGS} -I m4
 
-SUBDIRS = docs lib man tools scripts benchmarks demos overlay
+SUBDIRS = lib man tools scripts benchmarks demos overlay
 
 if BUILD_ASSEMBLER
 SUBDIRS += assembler
@@ -35,6 +35,8 @@
 SUBDIRS += tests
 endif
 
+SUBDIRS += docs
+
 MAINTAINERCLEANFILES = ChangeLog INSTALL
 
 .PHONY: ChangeLog INSTALL