[6.0] Fix incorrectly-specified platform list in CMake file. (swiftlang#646)

**Explanation:** Correctly sets `SWT_NO_EXIT_TESTS` on platforms that
don't support them when building with CMake.
**Scope:** Building iOS, watchOS, tvOS, visionOS, WASI from OSS.
**Issue:** N/A
**Original PR:** swiftlang#633
**Risk:** Low
**Testing:** Manually tested as we don't have CI using CMake yet.
**Reviewer:** @compnerd @briancroom

Author: grynspan

cmake/modules/shared/CompilerSettings.cmake

@@ -20,7 +20,8 @@ add_compile_options(
 if(APPLE)
   add_compile_definitions("SWT_TARGET_OS_APPLE")
 endif()
-if(CMAKE_SYSTEM_NAME IN_LIST "iOS;watchOS;tvOS;visionOS;WASI")
+set(SWT_NO_EXIT_TESTS_LIST "iOS" "watchOS" "tvOS" "visionOS" "WASI")
+if(CMAKE_SYSTEM_NAME IN_LIST SWT_NO_EXIT_TESTS_LIST)
   add_compile_definitions("SWT_NO_EXIT_TESTS")
 endif()
 if(NOT APPLE)