Changes for C to C++. Adding extern C to header files for compatibility.
diff --git a/config.m4 b/config.m4
index 72f8a1e..edd4c64 100644
--- a/config.m4
+++ b/config.m4
@@ -345,7 +345,7 @@
src/core/ext/filters/message_size/message_size_filter.c \
src/core/ext/filters/workarounds/workaround_cronet_compression_filter.c \
src/core/ext/filters/workarounds/workaround_utils.c \
- src/core/plugin_registry/grpc_plugin_registry.c \
+ src/core/plugin_registry/grpc_plugin_registry.cc \
src/boringssl/err_data.c \
third_party/boringssl/crypto/aes/aes.c \
third_party/boringssl/crypto/aes/key_wrap.c \