build: Run doxygen from the top build directory

Makefile.am

@@ -58,7 +58,7 @@ endif
 apidoc: stamp-doxygen
 
 stamp-doxygen: doc/doxygen.cfg src/libdvdcss.c src/dvdcss/dvdcss.h
-	cd doc && doxygen doxygen.cfg
+	doxygen $<
 	touch $@
 
 tools: test/csstest test/dvd_region

doc/doxygen.cfg.in

@@ -58,7 +58,7 @@ PROJECT_LOGO           =
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = @top_builddir@/doc
+OUTPUT_DIRECTORY       = @abs_builddir@
 
 # If the CREATE_SUBDIRS tag is set to YES, then doxygen will create 4096 sub-
 # directories (in 2 levels) under the output directory of each output format and
@@ -743,8 +743,8 @@ WARN_LOGFILE           =
 # spaces.
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = @top_srcdir@/src/dvdcss/dvdcss.h \
-                         @top_srcdir@/src/libdvdcss.c
+INPUT                  = @abs_top_srcdir@/src/dvdcss/dvdcss.h \
+                         @abs_top_srcdir@/src/libdvdcss.c
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses