SwiftScan: avoid swapping compilers

This library can and should be buildable with a standard compiler.
Disable the forced switch of the compiler.

Author: compnerd

tools/libSwiftScan/CMakeLists.txt

@@ -1,6 +1,3 @@
-include(SwiftWindowsSupport)
-swift_swap_compiler_if_needed("libSwiftScan")
-
 # Use an 'internal' name, this is primarily intended for SwiftDriver to import.
 set(SWIFT_SCAN_LIB_NAME "_InternalSwiftScan")