Disable "(Trusty) clang-3.8 compilation"

[lz4-c-compilers] contains the following command for clang-3.8.

```
make -C tests test-lz4
```

[lz4-c-compilers] 025c3ce8f9/.github/workflows/ci.yml (L17-L154)

.travis.yml

@@ -145,18 +145,18 @@ matrix:
 #     script:
 #       - make -C tests test-lz4 clean test-lz4c32 MOREFLAGS=-Werror
 #
-    - name: (Trusty) clang-3.8 compilation
-      dist: trusty
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.8
-          packages:
-            - clang-3.8
-      script:
-        - make -C tests test-lz4 CC=clang-3.8
-
+#   - name: (Trusty) clang-3.8 compilation
+#     dist: trusty
+#     addons:
+#       apt:
+#         sources:
+#           - ubuntu-toolchain-r-test
+#           - llvm-toolchain-precise-3.8
+#         packages:
+#           - clang-3.8
+#     script:
+#       - make -C tests test-lz4 CC=clang-3.8
+#
 #   - name: (Trusty) PowerPC + PPC64 compilation
 #     dist: trusty
 #     install: