added "objectivec" build target (#3033)

This target will be used by gRPC iOS bazel build system.

BUILD

@@ -797,3 +797,84 @@ proto_lang_toolchain(
     runtime = ":protobuf_java",
     visibility = ["//visibility:public"],
 )
+
+OBJC_HDRS = [
+    "objectivec/GPBArray.h",
+    "objectivec/GPBBootstrap.h",
+    "objectivec/GPBCodedInputStream.h",
+    "objectivec/GPBCodedOutputStream.h",
+    "objectivec/GPBDescriptor.h",
+    "objectivec/GPBDictionary.h",
+    "objectivec/GPBExtensionInternals.h",
+    "objectivec/GPBExtensionRegistry.h",
+    "objectivec/GPBMessage.h",
+    "objectivec/GPBProtocolBuffers.h",
+    "objectivec/GPBProtocolBuffers_RuntimeSupport.h",
+    "objectivec/GPBRootObject.h",
+    "objectivec/GPBRuntimeTypes.h",
+    "objectivec/GPBUnknownField.h",
+    "objectivec/GPBUnknownFieldSet.h",
+    "objectivec/GPBUtilities.h",
+    "objectivec/GPBWellKnownTypes.h",
+    "objectivec/GPBWireFormat.h",
+    "objectivec/google/protobuf/Any.pbobjc.h",
+    "objectivec/google/protobuf/Api.pbobjc.h",
+    "objectivec/google/protobuf/Duration.pbobjc.h",
+    "objectivec/google/protobuf/Empty.pbobjc.h",
+    "objectivec/google/protobuf/FieldMask.pbobjc.h",
+    "objectivec/google/protobuf/SourceContext.pbobjc.h",
+    "objectivec/google/protobuf/Struct.pbobjc.h",
+    "objectivec/google/protobuf/Timestamp.pbobjc.h",
+    "objectivec/google/protobuf/Type.pbobjc.h",
+    "objectivec/google/protobuf/Wrappers.pbobjc.h",
+]
+
+OBJC_PRIVATE_HDRS = [
+    "objectivec/GPBArray_PackagePrivate.h",
+    "objectivec/GPBCodedInputStream_PackagePrivate.h",
+    "objectivec/GPBCodedOutputStream_PackagePrivate.h",
+    "objectivec/GPBDescriptor_PackagePrivate.h",
+    "objectivec/GPBDictionary_PackagePrivate.h",
+    "objectivec/GPBMessage_PackagePrivate.h",
+    "objectivec/GPBRootObject_PackagePrivate.h",
+    "objectivec/GPBUnknownFieldSet_PackagePrivate.h",
+    "objectivec/GPBUnknownField_PackagePrivate.h",
+    "objectivec/GPBUtilities_PackagePrivate.h",
+]
+
+OBJC_SRCS = [
+    "objectivec/GPBArray.m",
+    "objectivec/GPBCodedInputStream.m",
+    "objectivec/GPBCodedOutputStream.m",
+    "objectivec/GPBDescriptor.m",
+    "objectivec/GPBDictionary.m",
+    "objectivec/GPBExtensionInternals.m",
+    "objectivec/GPBExtensionRegistry.m",
+    "objectivec/GPBMessage.m",
+    "objectivec/GPBRootObject.m",
+    "objectivec/GPBUnknownField.m",
+    "objectivec/GPBUnknownFieldSet.m",
+    "objectivec/GPBUtilities.m",
+    "objectivec/GPBWellKnownTypes.m",
+    "objectivec/GPBWireFormat.m",
+    "objectivec/google/protobuf/Any.pbobjc.m",
+    "objectivec/google/protobuf/Api.pbobjc.m",
+    "objectivec/google/protobuf/Duration.pbobjc.m",
+    "objectivec/google/protobuf/Empty.pbobjc.m",
+    "objectivec/google/protobuf/FieldMask.pbobjc.m",
+    "objectivec/google/protobuf/SourceContext.pbobjc.m",
+    "objectivec/google/protobuf/Struct.pbobjc.m",
+    "objectivec/google/protobuf/Timestamp.pbobjc.m",
+    "objectivec/google/protobuf/Type.pbobjc.m",
+    "objectivec/google/protobuf/Wrappers.pbobjc.m",
+]
+
+objc_library(
+    name = "objectivec",
+    hdrs = OBJC_HDRS + OBJC_PRIVATE_HDRS,
+    includes = [
+        "objectivec",
+    ],
+    non_arc_srcs = OBJC_SRCS,
+    visibility = ["//visibility:public"],
+)