[Pal/Linux-SGX] Add signing key as a build dependency

- pal-sgx-sign.py: add 'key' to dependecies
- clean up Makefile.manifest

Pal/src/host/Linux-SGX/Makefile.manifest

@@ -18,13 +18,13 @@ $(SGX_SIGNER_KEY):
 %.token: %.sig
 	$(call cmd,sgx_get_token)
 
-%.sig %.manifest.sgx: %.manifest % $(LIBPAL) $(SGX_SIGNER_KEY) %.manifest.sgx.d
+%.sig %.manifest.sgx: %.manifest % %.manifest.sgx.d
 	$(call cmd,sgx_sign_exec)
 
-%.sig %.manifest.sgx: manifest % $(LIBPAL) $(SGX_SIGNER_KEY) %.manifest.sgx.d
+%.sig %.manifest.sgx: manifest % %.manifest.sgx.d
 	$(call cmd,sgx_sign_exec)
 
-%.sig %.manifest.sgx: %.manifest $(LIBPAL) $(SGX_SIGNER_KEY) %.manifest.sgx.d
+%.sig %.manifest.sgx: %.manifest %.manifest.sgx.d
 	$(call cmd,sgx_sign)
 
 .PRECIOUS: %.manifest.sgx.d

Pal/src/host/Linux-SGX/signer/pal_sgx_sign.py

@@ -918,6 +918,7 @@ def make_depend(args):
                                          do_checksum=False).values():
         dependencies.add(filename[1])
     dependencies.add(args['libpal'])
+    dependencies.add(args['key'])
 
     with open(output, 'w') as file:
         manifest_sgx = output