cmake: fix building with CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON

This CMake global custom option tells it to find dependencies as cmake
Configs first, and only then look for `Find*` modules. This may result
in `find_package()` succeeding, but without actually creating `CURL::*`
imported targets the curl build scripts are expecting.

For dependencies with curl-specific, local, `Find*` modules, we always
want to use them, via the module detection method, and never a
Config-based detection. Ensure this by passing the `MODULE` option to
`find_package()` and `find_dependency()` to make them use `Find*`
modules unconditionally, making them work as expected with the
`CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON` option set.

curl uses local Find modules for all dependencies except OpenSSL and
ZLIB. The latter two keep using either CMake's built-in Find modules or
Config method as before this patch.

Also:

- apply the same change to `curl-config.cmake`. To fix consuming curl
  with this option set.
  Authored-by: Valerie Snyder
  Ref: #20764
  Follow-up to 16f073ef49 #16973

- GHA/distcheck: add a job testing both building and consuming curl with
  this option set. (takes 15 seconds)
  Use custom NGHTTP2 configuration for an extra twist (not required
  to trigger this issue.)
  Follow-up to fcde8d7e37 #20773

Reported-by: Valerie Snyder
Fixes #20729

Closes #20784

CMake/Macros.cmake

@@ -71,9 +71,17 @@ macro(curl_dependency_option _option_name _find_name _desc_name)
   set_property(CACHE ${_option_name} PROPERTY STRINGS "AUTO" "ON" "OFF")
 
   if(${_option_name} STREQUAL "AUTO")
-    find_package(${_find_name})
+    if(_find_name STREQUAL "ZLIB")
+      find_package(${_find_name})
+    else()
+      find_package(${_find_name} MODULE)
+    endif()
   elseif(${_option_name})
-    find_package(${_find_name} REQUIRED)
+    if(_find_name STREQUAL "ZLIB")
+      find_package(${_find_name} REQUIRED)
+    else()
+      find_package(${_find_name} MODULE REQUIRED)
+    endif()
   else()
     string(TOUPPER "${_find_name}" _find_name_upper)
     set(${_find_name}_FOUND OFF)  # cmake-lint: disable=C0103

CMake/curl-config.in.cmake

@@ -62,89 +62,89 @@ set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR} ${CMAKE_MODULE_PATH})
 set(_curl_libs "")
 
 if("@HAVE_BROTLI@")
-  find_dependency(Brotli)
+  find_dependency(Brotli MODULE)
   list(APPEND _curl_libs CURL::brotli)
 endif()
 if("@USE_ARES@")
-  find_dependency(Cares)
+  find_dependency(Cares MODULE)
   list(APPEND _curl_libs CURL::cares)
 endif()
 if("@HAVE_GSSAPI@")
-  find_dependency(GSS)
+  find_dependency(GSS MODULE)
   list(APPEND _curl_libs CURL::gss)
 endif()
 if("@USE_BACKTRACE@")
-  find_dependency(Libbacktrace)
+  find_dependency(Libbacktrace MODULE)
   list(APPEND _curl_libs CURL::libbacktrace)
 endif()
 if("@USE_GSASL@")
-  find_dependency(Libgsasl)
+  find_dependency(Libgsasl MODULE)
   list(APPEND _curl_libs CURL::libgsasl)
 endif()
 if(NOT "@USE_WIN32_LDAP@" AND NOT "@CURL_DISABLE_LDAP@")
-  find_dependency(LDAP)
+  find_dependency(LDAP MODULE)
   list(APPEND _curl_libs CURL::ldap)
 endif()
 if("@HAVE_LIBIDN2@")
-  find_dependency(Libidn2)
+  find_dependency(Libidn2 MODULE)
   list(APPEND _curl_libs CURL::libidn2)
 endif()
 if("@USE_LIBPSL@")
-  find_dependency(Libpsl)
+  find_dependency(Libpsl MODULE)
   list(APPEND _curl_libs CURL::libpsl)
 endif()
 if("@USE_LIBRTMP@")
-  find_dependency(Librtmp)
+  find_dependency(Librtmp MODULE)
   list(APPEND _curl_libs CURL::librtmp)
 endif()
 if("@USE_LIBSSH@")
-  find_dependency(Libssh)
+  find_dependency(Libssh MODULE)
   list(APPEND _curl_libs CURL::libssh)
 endif()
 if("@USE_LIBSSH2@")
-  find_dependency(Libssh2)
+  find_dependency(Libssh2 MODULE)
   list(APPEND _curl_libs CURL::libssh2)
 endif()
 if("@USE_LIBUV@")
-  find_dependency(Libuv)
+  find_dependency(Libuv MODULE)
   list(APPEND _curl_libs CURL::libuv)
 endif()
 if("@USE_MBEDTLS@")
-  find_dependency(MbedTLS)
+  find_dependency(MbedTLS MODULE)
   list(APPEND _curl_libs CURL::mbedtls)
 endif()
 if("@USE_NGHTTP2@")
-  find_dependency(NGHTTP2)
+  find_dependency(NGHTTP2 MODULE)
   list(APPEND _curl_libs CURL::nghttp2)
 endif()
 if("@USE_NGHTTP3@")
-  find_dependency(NGHTTP3)
+  find_dependency(NGHTTP3 MODULE)
   list(APPEND _curl_libs CURL::nghttp3)
 endif()
 if("@USE_NGTCP2@")
-  find_dependency(NGTCP2)
+  find_dependency(NGTCP2 MODULE)
   list(APPEND _curl_libs CURL::ngtcp2)
 endif()
 if("@USE_GNUTLS@")
-  find_dependency(GnuTLS)
+  find_dependency(GnuTLS MODULE)
   list(APPEND _curl_libs CURL::gnutls)
-  find_dependency(Nettle)
+  find_dependency(Nettle MODULE)
   list(APPEND _curl_libs CURL::nettle)
 endif()
 if("@USE_QUICHE@")
-  find_dependency(Quiche)
+  find_dependency(Quiche MODULE)
   list(APPEND _curl_libs CURL::quiche)
 endif()
 if("@USE_RUSTLS@")
-  find_dependency(Rustls)
+  find_dependency(Rustls MODULE)
   list(APPEND _curl_libs CURL::rustls)
 endif()
 if("@USE_WOLFSSL@")
-  find_dependency(WolfSSL)
+  find_dependency(WolfSSL MODULE)
   list(APPEND _curl_libs CURL::wolfssl)
 endif()
 if("@HAVE_ZSTD@")
-  find_dependency(Zstd)
+  find_dependency(Zstd MODULE)
   list(APPEND _curl_libs CURL::zstd)
 endif()