build: support aliases for TARGET_SDKS

Introduce two new aliasees `ALL_POSIX_PLATFORMS` and `ALL_APPLE_PLATFORMS`.  The
latter expands to iOS, tvOS, watchOS, macOS and if relevant, the simulators.
The former expands to the same list as `ALL_APPLE_PLATFORMS` as well as Linux
and FreeBSD.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -1111,6 +1111,8 @@ function(add_swift_library name)
   if("${SWIFTLIB_TARGET_SDKS}" STREQUAL "")
     set(SWIFTLIB_TARGET_SDKS ${SWIFT_SDKS})
   endif()
+  list_replace(SWIFTLIB_TARGET_SDKS ALL_POSIX_PLATFORMS "ALL_APPLE_PLATFORMS;ANDROID;CYGWIN;FREEBSD;LINUX")
+  list_replace(SWIFTLIB_TARGET_SDKS ALL_APPLE_PLATFORMS "IOS;IOS_SIMULATOR;TVOS;TVOS_SIMULATOR;WATCHOS;WATCHOS_SIMULATOR;OSX")
 
   # All Swift code depends on the standard library, except for the standard
   # library itself.

cmake/modules/SwiftList.cmake

@@ -48,3 +48,15 @@ function(_list_escape_for_shell input_list result_var_name)
   set("${result_var_name}" "${result}" PARENT_SCOPE)
 endfunction()
 
+function(list_replace input_list old new)
+  set(replaced_list)
+  foreach(item ${${input_list}})
+    if(${item} STREQUAL ${old})
+      list(APPEND replaced_list ${new})
+    else()
+      list(APPEND replaced_list ${item})
+    endif()
+  endforeach()
+  set("${input_list}" "${replaced_list}" PARENT_SCOPE)
+endfunction()
+