Use strip_import_prefix for wkp instead of copying them

Cherry-pick of: https://github.com/protocolbuffers/protobuf/pull/6403

Partial commit for third_party/*, see #8962.

Signed-off-by: iirina <elenairina@google.com>

third_party/protobuf/3.6.1/BUILD

diff --git a/third_party/protobuf/3.6.1/BUILD b/third_party/protobuf/3.6.1/BUILD
index 02fe5ba..a24d0c9 100644
--- a/third_party/protobuf/3.6.1/BUILD
+++ b/third_party/protobuf/3.6.1/BUILD
@@ -245,23 +245,21 @@
 # Map of all well known protos.
 # name => (include path, imports)
 WELL_KNOWN_PROTO_MAP = {
-    "any" : ("google/protobuf/any.proto", []),
-    "api" : ("google/protobuf/api.proto", ["source_context", "type"]),
-    "compiler_plugin" : ("google/protobuf/compiler/plugin.proto", ["descriptor"]),
-    "descriptor" : ("google/protobuf/descriptor.proto", []),
-    "duration" : ("google/protobuf/duration.proto", []),
-    "empty" : ("google/protobuf/empty.proto", []),
-    "field_mask" : ("google/protobuf/field_mask.proto", []),
-    "source_context" : ("google/protobuf/source_context.proto", []),
-    "struct" : ("google/protobuf/struct.proto", []),
-    "timestamp" : ("google/protobuf/timestamp.proto", []),
-    "type" : ("google/protobuf/type.proto", ["any", "source_context"]),
-    "wrappers" : ("google/protobuf/wrappers.proto", []),
+    "any" : ("src/google/protobuf/any.proto", []),
+    "api" : ("src/google/protobuf/api.proto", ["source_context", "type"]),
+    "compiler_plugin" : ("src/google/protobuf/compiler/plugin.proto", ["descriptor"]),
+    "descriptor" : ("src/google/protobuf/descriptor.proto", []),
+    "duration" : ("src/google/protobuf/duration.proto", []),
+    "empty" : ("src/google/protobuf/empty.proto", []),
+    "field_mask" : ("src/google/protobuf/field_mask.proto", []),
+    "source_context" : ("src/google/protobuf/source_context.proto", []),
+    "struct" : ("src/google/protobuf/struct.proto", []),
+    "timestamp" : ("src/google/protobuf/timestamp.proto", []),
+    "type" : ("src/google/protobuf/type.proto", ["any", "source_context"]),
+    "wrappers" : ("src/google/protobuf/wrappers.proto", []),
 }
 
-RELATIVE_WELL_KNOWN_PROTOS = [proto[1][0] for proto in WELL_KNOWN_PROTO_MAP.items()]
-
-WELL_KNOWN_PROTOS = ["src/" + s for s in RELATIVE_WELL_KNOWN_PROTOS]
+WELL_KNOWN_PROTOS = [value[0] for value in WELL_KNOWN_PROTO_MAP.values()]
 
 filegroup(
     name = "well_known_protos",
@@ -291,17 +289,10 @@
 # )
 ################################################################################
 
-internal_copied_filegroup(
-    name = "_internal_wkt_protos",
-    srcs = WELL_KNOWN_PROTOS,
-    dest = "",
-    strip_prefix = "src",
-    visibility = ["//visibility:private"],
-)
-
 [proto_library(
     name = proto[0] + "_proto",
     srcs = [proto[1][0]],
+    strip_import_prefix = "src",
     deps = [dep + "_proto" for dep in proto[1][1]],
     visibility = ["//visibility:public"],
     ) for proto in WELL_KNOWN_PROTO_MAP.items()]
@@ -714,7 +705,7 @@
 
 # TODO(dzc): Remove this once py_proto_library can have labels in srcs, in
 # which case we can simply add :protos_python in srcs.
-COPIED_WELL_KNOWN_PROTOS = ["python/" + s for s in RELATIVE_WELL_KNOWN_PROTOS]
+COPIED_WELL_KNOWN_PROTOS = ["python/" + s[4:] for s in WELL_KNOWN_PROTOS]
 
 py_proto_library(
     name = "protobuf_python",