ocaml: Fix and enable parallel builds.

We only have to serialize the two calls to ocamlmklib, since both will
try to create a file called 'libmlguestfs.a'.  Apart from that,
parallel builds here should be fine.

.gitignore

@@ -266,6 +266,7 @@ Makefile.in
 /ocaml/guestfs.mli
 /ocamlinit-stamp
 /ocaml/META
+/ocaml/stamp-mlguestfs
 /ocaml/t/guestfs_005_load.bc
 /ocaml/t/guestfs_005_load.opt
 /ocaml/t/guestfs_010_basic.bc

ocaml/Makefile.am

@@ -53,15 +53,22 @@ noinst_DATA = mlguestfs.cma mlguestfs.cmxa META
 # library; we link with the object files that it generates.
 noinst_LIBRARIES = libguestfsocaml.a
 
-mlguestfs.cma: libguestfsocaml.a guestfs.cmo
+# Note that both calls to ocamlmklib below will create
+# 'libmlguestfs.a' and if run at the same time, they will stomp on or
+# corrupt each others copy.  Hence we have to serialize the calls.
+
+CLEANFILES += stamp-mlguestfs
+
+mlguestfs.cma mlguestfs.cmxa: stamp-mlguestfs
+
+stamp-mlguestfs: libguestfsocaml.a guestfs.cmo guestfs.cmx
 	$(OCAMLMKLIB) -o mlguestfs \
 	  $(libguestfsocaml_a_OBJECTS) guestfs.cmo \
 	  -L$(top_builddir)/src/.libs -lguestfs
-
-mlguestfs.cmxa: libguestfsocaml.a guestfs.cmx
 	$(OCAMLMKLIB) -o mlguestfs \
 	  $(libguestfsocaml_a_OBJECTS) guestfs.cmx \
 	  -L$(top_builddir)/src/.libs -lguestfs
+	touch $@
 
 libguestfsocaml_a_CPPFLAGS = \
 	-DGUESTFS_PRIVATE=1 \
@@ -235,7 +242,3 @@ install-data-hook:
 CLEANFILES += $(noinst_DATA)
 
 endif
-
-# Tell version 3.79 and up of GNU make to not build goals in this
-# directory in parallel.  (Possible solution for RHBZ#502309).
-.NOTPARALLEL: