Fix symbol duplication on Xcode/clang (tensorflow#4504)

tyfkda · gunan · commit b5a169f3e307 · 2016-10-24T09:45:50.000-07:00
Following linker error happened on Xcode:

```
duplicate symbol __Z14tf_git_versionv in:
    /Users/admin/tmp/tensorflow/tensorflow/contrib/ios_examples/simple/../../makefile/gen/lib/libtensorflow-core.a(version_info.o)
duplicate symbol __Z19tf_compiler_versionv in:
    /Users/admin/tmp/tensorflow/tensorflow/contrib/ios_examples/simple/../../makefile/gen/lib/libtensorflow-core.a(version_info.o)
ld: 2 duplicate symbols for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

These functions are defined in `tensorflow/core/util/version_info.cc`.
It seems an object file for it is added twice in Makefile:
(`$(wildcard tensorflow/core/util/*.cc)` and `$(tensorflow/core/util/version_info.cc)
`)
diff --git a/tensorflow/contrib/makefile/Makefile b/tensorflow/contrib/makefile/Makefile
@@ -426,6 +426,8 @@ $(wildcard tensorflow/core/platform/*/*/*.cc) \
 $(wildcard tensorflow/core/util/*.cc) \
 $(wildcard tensorflow/core/util/*/*.cc) \
 tensorflow/core/util/version_info.cc
+# Remove duplicates (for version_info.cc)
+CORE_CC_ALL_SRCS := $(sort $(CORE_CC_ALL_SRCS))
 CORE_CC_EXCLUDE_SRCS := \
 $(wildcard tensorflow/core/*/*test.cc) \
 $(wildcard tensorflow/core/*/*testutil*) \
