MONGOCRYPT-839 address CMP0169 for CMake 3.30 and newer (#1053)

Author: eramongodb

CHANGELOG.md

@@ -5,6 +5,10 @@
 ### Changed
 
 - Set CMake minimum required version to `3.15...4.0` (with maximum policy version set to `4.0`).
+- `FetchContent_MakeAvailable()` is used to populate dependencies instead of `FetchContent_Populate()`.
+  - This applies to MongoDB C Driver when `MONGOCRYPT_MONGOC_DIR` is not set to `USE-SYSTEM`.
+  - This applies to IntelDFP when `MONGOCRYPT_DFP_DIR` is not set to `USE-SYSTEM`.
+  - Note: `FetchContent_Populate()` is still used for CMake versions prior to 3.18 to avoid `add_subdirectory()` behavior.
 
 ## 1.15.0
 

cmake/FetchMongoC.cmake

@@ -27,12 +27,18 @@ FetchContent_Declare (
     embedded_mcd
     URL "https://github.com/mongodb/mongo-c-driver/archive/refs/tags/${MONGOC_FETCH_TAG_FOR_LIBBSON}.tar.gz"
     PATCH_COMMAND ${patch_command} --verbose
+    SOURCE_SUBDIR "NO_ADD_SUBDIRECTORY" # add_subdirectory() is handled by ImportBSON.cmake.
     )
 # Populate it:
 FetchContent_GetProperties (embedded_mcd)
 if (NOT embedded_mcd_POPULATED)
     message (STATUS "Downloading mongo-c-driver ${MONGOC_FETCH_TAG_FOR_LIBBSON} for libbson")
-    FetchContent_Populate (embedded_mcd)
+    if("${CMAKE_VERSION}" VERSION_LESS "3.18.0")
+        # SOURCE_SUBDIR is not yet supported.
+        FetchContent_Populate(embedded_mcd)
+    else()
+        FetchContent_MakeAvailable(embedded_mcd)
+    endif()
 endif ()
 # Store the directory path to the external mongoc project:
 get_filename_component (MONGOCRYPT_MONGOC_DIR "${embedded_mcd_SOURCE_DIR}" ABSOLUTE)

cmake/IntelDFP.cmake

@@ -44,12 +44,18 @@ FetchContent_Declare (
     URL "${_default_url}"
     ${_hash_arg}
     PATCH_COMMAND ${patch_command} --verbose
+    SOURCE_SUBDIR "NO_ADD_SUBDIRECTORY" # Targets are manually defined below.
     )
 
 FetchContent_GetProperties (intel_dfp)
 if (NOT intel_dfp_POPULATED)
     message (STATUS "Obtaining Intel Decimal FP library: ${INTEL_DFP_LIBRARY_URL}")
-    FetchContent_Populate (intel_dfp)
+    if("${CMAKE_VERSION}" VERSION_LESS "3.18.0")
+        # SOURCE_SUBDIR is not yet supported.
+        FetchContent_Populate(intel_dfp)
+    else()
+        FetchContent_MakeAvailable(intel_dfp)
+    endif()
 endif ()
 
 # This list of sources was generated by copying the MongoDB server and removing any unnecessary.