Introduce Proto C API; based on cl/198113115 by amauryfa
diff --git a/BUILD b/BUILD
index 191ab92..48c5aa7 100644
--- a/BUILD
+++ b/BUILD
@@ -689,6 +689,7 @@
     linkstatic = 1,
     deps = [
         ":protobuf",
+        ":proto_api",
     ] + select({
         "//conditions:default": [],
         ":use_fast_cpp_protos": ["//external:python_headers"],
@@ -831,6 +832,15 @@
     deps = [":python_tests"],
 )
 
+cc_library(
+    name = "proto_api",
+    hdrs = ["python/google/protobuf/proto_api.h"],
+    deps = [
+        ":protobuf_python",
+        "//external:python_headers",
+    ],
+)
+
 proto_lang_toolchain(
     name = "cc_toolchain",
     command_line = "--cpp_out=$(OUT)",