CDRIVER-4233 fix implicit decl of arc4random and strlcpy on macOS (#910)

Author: kevinAlbs

src/libbson/CMakeLists.txt

@@ -36,7 +36,17 @@ set (CPACK_PACKAGE_VERSION_MAJOR ${BSON_MAJOR_VERSION})
 set (CPACK_PACKAGE_VERSION_MINOR ${BSON_MINOR_VERSION})
 
 # Enable X/Open 7.0 / POSIX 2008
-add_compile_options($<$<NOT:$<PLATFORM_ID:Windows>>:-D_XOPEN_SOURCE=700>)
+if (NOT WIN32)
+   add_compile_options(-D_XOPEN_SOURCE=700)
+   # Add to CMAKE_REQUIRED_DEFINITIONS to apply to CHECK_SYMBOL_EXISTS.
+   set (CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS} -D_XOPEN_SOURCE=700")
+endif ()
+# Enable macOS extensions for strlcpy and arc4random.
+if (APPLE)
+   add_compile_options(-D_DARWIN_C_SOURCE=1)
+   # Add to CMAKE_REQUIRED_DEFINITIONS to apply to CHECK_SYMBOL_EXISTS.
+   set (CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS} -D_DARWIN_C_SOURCE=1")
+endif ()
 
 include (CPack)
 TEST_BIG_ENDIAN (BSON_BIG_ENDIAN)