Temporary disable Travis s390x Makefile build (#9512)

Summary:
Due to some unexplained errors with gcc-7

```
Assembler messages:
Error: invalid switch -march=z14
Error: unrecognized option -march=z14
```

Relevant to https://github.com/facebook/rocksdb/issues/9388

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9512

Test Plan: CI

Reviewed By: hx235

Differential Revision: D34044989

Pulled By: pdillinger

fbshipit-source-id: a5406e8f30b2b187949f75c8cee4e2a0eb976670

.travis.yml

@@ -58,6 +58,10 @@ matrix:
     env: JOB_NAME=cmake-mingw
   - os: linux
     compiler: clang
+  - if: type = pull_request AND commit_message !~ /FULL_CI/
+    os: linux
+    arch: s390x # Temporary while working through gcc-7 + assembler issue
+    env: TEST_GROUP=platform_dependent
   - if: type = pull_request AND commit_message !~ /FULL_CI/
     os: linux
     arch: arm64