[CMake] Fatal error when bootstrapping is not "hosttools"

and Swift parser integration is enabled.
If swift parser integration is enabled, SwiftSyntax libraries are always
built with host tools. Other SwiftCompilerSources modules must use the
same runtime with parser libraries.

Author: rintaro

CMakeLists.txt

@@ -953,6 +953,10 @@ if(SWIFT_PATH_TO_EARLYSWIFTSYNTAX_BUILD_DIR)
   else()
     set(SWIFT_SWIFT_PARSER TRUE)
     include(${SWIFT_PATH_TO_EARLYSWIFTSYNTAX_TARGETS})
+
+    if(SWIFT_HOST_VARIANT_SDK STREQUAL "LINUX" AND NOT BOOTSTRAPPING_MODE STREQUAL "HOSTTOOLS")
+      message(FATAL_ERROR "Only BOOTSTRAPPING=HOSTTOOLS is supported in Linux when Swift parser integration is enabled")
+    endif()
   endif()
 endif()