[SwiftCore] Enable explicit module builds

Explicit module builds help prevent the dependency scanner from getting
lost and attempting to pull the SwiftShims module from the resource
directory, existing SDK, and the just-built standard library.
They aren't part of the library interface, but make it possible to build
the runtime libraries without seeing duplicate shims. Moving the flag to
a top-level compile command.

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -176,6 +176,7 @@ add_compile_options(
 add_link_options($<$<PLATFORM_ID:Windows>:LINKER:/WX>)
 
 add_compile_options(
+  $<$<COMPILE_LANGUAGE:Swift>:-explicit-module-build>
   "$<$<COMPILE_LANGUAGE:Swift>:-nostdlibimport>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-library-level api>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-runtime-compatibility-version none>"

Runtimes/Core/core/CMakeLists.txt

@@ -290,7 +290,6 @@ target_compile_options(swiftCore PRIVATE
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature AddressableTypes>"
   $<$<COMPILE_LANGUAGE:Swift>:-parse-stdlib>
   $<$<COMPILE_LANGUAGE:Swift>:-nostdimport>
-  $<$<COMPILE_LANGUAGE:Swift>:-explicit-module-build>
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -group-info-path -Xfrontend ${CMAKE_CURRENT_SOURCE_DIR}/GroupInfo.json>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -disable-objc-attr-requires-foundation-module>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -require-explicit-availability=ignore>")