cmcurl: Backport curl bug 1192 fix (#14250)

LLVM headers define strlcat as a macro rather than as a function.
See upstream Curl issue:

 http://curl.haxx.se/bug/view.cgi?id=1192

It was addressed by removing use of strlcat altogether.  Port the
upstream fix to CMake's curl.
Merge topic 'curl-bug-1192' into next

e643e02 cmcurl: Backport curl bug 1192 fix (#14250)