Merge pull request #1034 from sunxiaoguang/fix_duplicated_symbols

src/php/ext/grpc/call.c

src/php/ext/grpc/call.h

src/php/ext/grpc/channel.c

src/php/ext/grpc/channel.h

src/php/ext/grpc/completion_queue.c

src/php/ext/grpc/completion_queue.h

src/php/ext/grpc/credentials.c

src/php/ext/grpc/credentials.h

src/php/ext/grpc/server.c

src/php/ext/grpc/server.h

src/php/ext/grpc/server_credentials.c

src/php/ext/grpc/server_credentials.h

src/php/ext/grpc/timeval.c

src/php/ext/grpc/timeval.h