build: correct variable in SDK configuration

The variable was supported to be set to the triple, except it was set to
the variable itself, effectively setting the variable to nothing.  This
is needed to clear the path to directory style installation for
non-Apple targets.

cmake/modules/SwiftConfigureSDK.cmake

@@ -374,7 +374,7 @@ macro(configure_sdk_unix name architectures)
 
     # If the module triple wasn't set explicitly, it's the same as the triple.
     if(NOT SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE)
-      set(SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE "${SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE}")
+      set(SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE "${SWIFT_SDK_${prefix}_ARCH_${arch}_TRIPLE}")
     endif()
   endforeach()
 
@@ -407,7 +407,7 @@ macro(configure_sdk_windows name environment architectures)
           "${arch}-unknown-windows-${environment}")
     endif()
 
-    set(SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE "${SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE}")
+    set(SWIFT_SDK_${prefix}_ARCH_${arch}_MODULE "${SWIFT_SDK_${prefix}_ARCH_${arch}_TRIPLE}")
 
     # NOTE: set the path to / to avoid a spurious `--sysroot` from being passed
     # to the driver -- rely on the `INCLUDE` AND `LIB` environment variables