I've recently been getting these build warnings with MSVC.

Brett, could this have been due to https://chromium.googlesource.com/chromium/src/+/39d6ba4eece90cc70bff87f2ecc39e5a790e1233 ?  That seems like a plausible recent culprit.

generated.lib(cloud_policy_generated.obj) : warning LNK4217: locally defined symbol ??1ExternalDataFetcher@policy@@QEAA@XZ (public: __cdecl policy::ExternalDataFetcher::~ExternalDataFetcher(void)) imported in function "public: void * __cdecl policy::ExternalDataFetcher::`scalar deleting destructor'(unsigned int)" (??_GExternalDataFetcher@policy@@QEAAPEAXI@Z)

generated.lib(cloud_policy_generated.obj) : warning LNK4217: locally defined symbol ?Set@PolicyMap@policy@@QEAAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@W4PolicyLevel@2@W4PolicyScope@2@W4PolicySource@2@V?$unique_ptr@VValue@base@@U?$default_delete@VValue@base@@@std@@@4@V?$unique_ptr@VExternalDataFetcher@policy@@U?$default_delete@VExternalDataFetcher@policy@@@std@@@4@@Z (public: void __cdecl policy::PolicyMap::Set(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,enum policy::PolicyLevel,enum policy::PolicyScope,enum policy::PolicySource,class std::unique_ptr<class
base::Value,struct std::default_delete<class base::Value> >,class std::unique_ptr<class policy::ExternalDataFetcher,struct std::default_delete<class policy::ExternalDataFetcher> >)) imported in function "void __cdecl policy::DecodePolicy(class enterprise_management::CloudPolicySettings const &,class base::WeakPtr<class policy::CloudExternalDataManager>,class policy::PolicyMap *)" (?DecodePolicy@policy@@YAXAEBVCloudPolicySettings@enterprise_management@@V?$WeakPtr@VCloudExternalDataManager@policy@@@base@@PEAVPolicyMap@1@@Z)