Missing some #include?
#include
C:\buildkite-agent\builds\windows-3\objectx\cmake\Utilities\cmcurl\lib\curl_sspi.c(155,29): error C2065: 'strdup': undeclared identifier [C:\buildkite-agent\builds\windows-3\objectx\cmake\00.BUILD\Stage1\Utilities\cmcurl\lib\cmcurl.vcxproj]
Thanks for the report. It looks like something is up with curl_multibyte.h here. It seems that WIN32 is no longer defined? In any case, that #else should probably #include <string.h> for its impls.
curl_multibyte.h
WIN32
#else
#include <string.h>
FYI @brad.king