doc: fix generating doxy with out-of-tree builds

Broken in 753930bc73, as the path to
Doxyfile passed to doxy-wrapper.sh is relative to the build dir, while
the recipe cd's to the source dir before invoking the wrapper.

doc/Makefile

@@ -102,7 +102,7 @@ DOXY_INPUT_DEPS = $(addprefix $(SRC_PATH)/, $(DOXY_INPUT)) ffbuild/config.mak
 
 doc/doxy/html: TAG = DOXY
 doc/doxy/html: $(SRC_PATH)/doc/Doxyfile $(SRC_PATH)/doc/doxy-wrapper.sh $(DOXY_INPUT_DEPS)
-	$(M)OUT_DIR=$$PWD/doc/doxy; cd $(SRC_PATH); ./doc/doxy-wrapper.sh $$OUT_DIR $< $(DOXYGEN) $(DOXY_INPUT);
+	$(M)$(SRC_PATH)/doc/doxy-wrapper.sh $$PWD/doc/doxy $(SRC_PATH) doc/Doxyfile $(DOXYGEN) $(DOXY_INPUT);
 
 install-doc: install-html install-man
 

doc/doxy-wrapper.sh

@@ -1,10 +1,13 @@
 #!/bin/sh
 
 OUT_DIR="${1}"
-DOXYFILE="${2}"
-DOXYGEN="${3}"
+SRC_DIR="${2}"
+DOXYFILE="${3}"
+DOXYGEN="${4}"
 
-shift 3
+shift 4
+
+cd ${SRC_DIR}
 
 if [ -e "VERSION" ]; then
     VERSION=`cat "VERSION"`