[Examples] Don't use unsupported "Rules with Grouped Targets" in Make

This commit is a result of debugging a rare race condition during build
of some of our examples, which resulted in "enclave EINIT failed -
Invalid measurement" error.

It turns out that Make in versions that doesn't support the `&:`
operator ("Rules with Grouped Targets") silently ignores it and calls
the recipe for each target separately, without even a warning.

Signed-off-by: Michał Kowalczyk <mkow@invisiblethingslab.com>

Examples/blender/Makefile

@@ -59,7 +59,12 @@ blender.manifest: blender.manifest.template trusted-libs | $(RUN_DIR)
 	     $<; \
     cat trusted-libs) > $@
 
-blender.sig blender.manifest.sgx &: $(BLENDER_DIR)/blender blender.manifest \
+# Make on Ubuntu <= 20.04 doesn't support "Rules with Grouped Targets" (`&:`),
+# we need to hack around.
+blender.sig blender.manifest.sgx: sgx_outputs
+
+.INTERMEDIATE: sgx_outputs
+sgx_outputs: $(BLENDER_DIR)/blender blender.manifest \
         $(GRAPHENE_DIR)/Runtime/libpal-Linux-SGX.so | $(RUN_DIR)
 	$(GRAPHENE_DIR)/Pal/src/host/Linux-SGX/signer/pal-sgx-sign \
 		-output blender.manifest.sgx \

Examples/gcc/Makefile

@@ -54,9 +54,12 @@ trusted-libs: ../common_tools/get_deps.sh
 		$<; \
 	cat trusted-libs) > $@
 
-# Rules to generate the SGX-specific manifest (.manifest.sgx), the enclave signature (.sig), and the
-# enclave initialization token (.token).
-gcc.sig gcc.manifest.sgx &: gcc.manifest
+# Make on Ubuntu <= 20.04 doesn't support "Rules with Grouped Targets" (`&:`),
+# we need to hack around.
+gcc.sig gcc.manifest.sgx: sgx_outputs
+
+.INTERMEDIATE: sgx_outputs
+sgx_outputs: gcc.manifest
 	$(GRAPHENEDIR)/Pal/src/host/Linux-SGX/signer/pal-sgx-sign \
 		-libpal $(GRAPHENEDIR)/Runtime/libpal-Linux-SGX.so \
 		-key $(SGX_SIGNER_KEY) \

Examples/pytorch/Makefile

@@ -49,7 +49,12 @@ include ../../Scripts/Makefile.configs
 		-e 's|$$(ARCH_LIBDIR)|'"$(ARCH_LIBDIR)"'|g' \
 		$< > $@
 
-pytorch.sig pytorch.manifest.sgx &: pytorch.manifest
+# Make on Ubuntu <= 20.04 doesn't support "Rules with Grouped Targets" (`&:`),
+# we need to hack around.
+pytorch.sig pytorch.manifest.sgx: sgx_outputs
+
+.INTERMEDIATE: sgx_outputs
+sgx_outputs: pytorch.manifest
 	$(GRAPHENEDIR)/Pal/src/host/Linux-SGX/signer/pal-sgx-sign \
 		-libpal $(GRAPHENEDIR)/Runtime/libpal-Linux-SGX.so \
 		-key $(SGX_SIGNER_KEY) \

Examples/redis/Makefile

@@ -89,7 +89,12 @@ redis-server.manifest: redis-server.manifest.template
 # EINITTOKEN must be generated on the machine where the application will run, not where it was
 # built.
 
-redis-server.sig redis-server.manifest.sgx &: redis-server.manifest $(SRCDIR)/src/redis-server
+# Make on Ubuntu <= 20.04 doesn't support "Rules with Grouped Targets" (`&:`),
+# we need to hack around.
+redis-server.sig redis-server.manifest.sgx: sgx_outputs
+
+.INTERMEDIATE: sgx_outputs
+sgx_outputs: redis-server.manifest $(SRCDIR)/src/redis-server
 	$(GRAPHENEDIR)/Pal/src/host/Linux-SGX/signer/pal-sgx-sign \
 		-libpal $(GRAPHENEDIR)/Runtime/libpal-Linux-SGX.so \
 		-key $(SGX_SIGNER_KEY) \