Ignore lexer.h auto-generated file

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/.gitignore b/.gitignore
index c9d90fb..f13ec27 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@
 /fio
 y.tab.*
 lex.yy.c
+lexer.h
diff --git a/Makefile b/Makefile
index 795f75c..3f8be4f 100644
--- a/Makefile
+++ b/Makefile
@@ -349,7 +349,7 @@
 	$(QUIET_LINK)$(CC) $(LDFLAGS) $(CFLAGS) -o $@ $(T_DEDUPE_OBJS) $(LIBS)
 
 clean: FORCE
-	@rm -f .depend $(FIO_OBJS) $(GFIO_OBJS) $(OBJS) $(T_OBJS) $(PROGS) $(T_PROGS) core.* core gfio FIO-VERSION-FILE *.d lib/*.d crc/*.d engines/*.d profiles/*.d t/*.d config-host.mak config-host.h y.tab.[ch] lex.yy.c exp/*.[do]
+	@rm -f .depend $(FIO_OBJS) $(GFIO_OBJS) $(OBJS) $(T_OBJS) $(PROGS) $(T_PROGS) core.* core gfio FIO-VERSION-FILE *.d lib/*.d crc/*.d engines/*.d profiles/*.d t/*.d config-host.mak config-host.h y.tab.[ch] lex.yy.c exp/*.[do] lexer.h
 
 distclean: clean FORCE
 	@rm -f cscope.out fio.pdf fio_generate_plots.pdf fio2gnuplot.pdf