Always link C++ objects into the surrounding Rust library

Author: dtolnay

BUCK

@@ -51,6 +51,7 @@ cxx_library(
     },
     exported_linker_flags = ["-lstdc++"],
     header_namespace = "rust",
+    preferred_linkage = "static",
     visibility = ["PUBLIC"],
 )
 

demo/BUCK

@@ -21,6 +21,7 @@ cxx_library(
     name = "blobstore-sys",
     srcs = ["src/blobstore.cc"],
     compiler_flags = ["-std=c++14"],
+    preferred_linkage = "static",
     deps = [
         ":blobstore-include",
         ":bridge/include",

tests/BUCK

@@ -38,6 +38,7 @@ cxx_library(
         "ffi/module.rs.h": ":module/header",
         "ffi/tests.h": "ffi/tests.h",
     },
+    preferred_linkage = "static",
 )
 
 rust_cxx_bridge(