Merge bitcoin#31231: cmake: Fix IF_CHECK_PASSED option handling

97a18c8 cmake: Fix `IF_CHECK_PASSED` option handling (Hennadii Stepanov)

Pull request description:

  `IF_CHECK_PASSED` is a multi-value keyword, resulting in a list value. Convert it to a string before applying any `string()` command.

  Split from bitcoin#30861.

  No current CMake code is affected by this bug.

ACKs for top commit:
  theuni:
    utACK 97a18c8

Tree-SHA512: d2556ca38c35a8992175e9f948c2028a789e71c2b2d5fdf365b31710c8ed3d5edf5d0363853c5d750d29abb58cfda3c78cdc2971a627e5b4c61aca4ec2a33356

cmake/module/TryAppendCXXFlags.cmake

@@ -72,7 +72,8 @@ function(try_append_cxx_flags flags)
         target_compile_options(${TACXXF_TARGET} INTERFACE ${TACXXF_IF_CHECK_PASSED})
       endif()
       if(DEFINED TACXXF_VAR)
-        string(STRIP "${${TACXXF_VAR}} ${TACXXF_IF_CHECK_PASSED}" ${TACXXF_VAR})
+        list(JOIN TACXXF_IF_CHECK_PASSED " " flags_if_check_passed_as_string)
+        string(STRIP "${${TACXXF_VAR}} ${flags_if_check_passed_as_string}" ${TACXXF_VAR})
       endif()
     else()
       if(DEFINED TACXXF_TARGET)

cmake/module/TryAppendLinkerFlag.cmake

@@ -48,7 +48,8 @@ function(try_append_linker_flag flag)
         target_link_options(${TALF_TARGET} INTERFACE ${TALF_IF_CHECK_PASSED})
       endif()
       if(DEFINED TALF_VAR)
-        string(STRIP "${${TALF_VAR}} ${TALF_IF_CHECK_PASSED}" ${TALF_VAR})
+        list(JOIN TALF_IF_CHECK_PASSED " " flags_if_check_passed_as_string)
+        string(STRIP "${${TALF_VAR}} ${flags_if_check_passed_as_string}" ${TALF_VAR})
       endif()
     else()
       if(DEFINED TALF_TARGET)