PPC/s390: [test] skip 2 tests for ppc and s390

These 2 test have known issues

Change-Id: I4830e0af0f4f1cf7fd1189316356dd1f7dc2c6eb
Reviewed-on: https://chromium-review.googlesource.com/896721Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#51074}

test/mjsunit/mjsunit.status

@@ -723,6 +723,9 @@
 
   # TODO(ppc/s390): implement atomic operations
   'wasm/atomics': [SKIP],
+  'wasm/shared-memory': [SKIP],
+  # TODO(ppc/s390): fix constant pool issue and use implement tagging
+  'wasm/compiled-module-serialization': [SKIP],
 }],  # 'arch == ppc64 or arch == ppc or arch == s390 or arch == s390x'
 
 ##############################################################################