fixed #12666 - got rid of ill-conceived USE_MATCHCOMPILER CMake option validation (#6348)

I went quite overboard when I introduced the validation of the define.
That was not necessary in CMake as we provide feedback on the usage of
the matchcompiler. So only handle the special options and otherwise rely
on the regular CMake logic.

Author: firewave

cmake/options.cmake

@@ -22,19 +22,23 @@ option(WARNINGS_ARE_ERRORS  "Treat warnings as errors"
 option(EXTERNALS_AS_SYSTEM  "Treat externals as system includes"                            OFF)
 
 set(USE_MATCHCOMPILER "Auto" CACHE STRING "Usage of match compiler")
-set(_MATCHCOMPILER_STRINGS Auto Off On Verify)
-set_property(CACHE USE_MATCHCOMPILER PROPERTY STRINGS ${_MATCHCOMPILER_STRINGS})
-if(NOT ${USE_MATCHCOMPILER} IN_LIST _MATCHCOMPILER_STRINGS)
-    message(FATAL_ERROR "Invalid USE_MATCHCOMPILER value '${USE_MATCHCOMPILER}'")
-endif()
-if(USE_MATCHCOMPILER STREQUAL "Auto")
-    if(NOT CMAKE_BUILD_TYPE STREQUAL "Debug")
-        set(USE_MATCHCOMPILER_OPT "On")
+set_property(CACHE USE_MATCHCOMPILER PROPERTY STRINGS Auto Off On Verify)
+if(USE_MATCHCOMPILER)
+    if(USE_MATCHCOMPILER STREQUAL "Auto")
+        if(NOT CMAKE_BUILD_TYPE STREQUAL "Debug")
+            message(STATUS "Non-debug build detected - enabling matchcompiler")
+            set(USE_MATCHCOMPILER_OPT "On")
+        else()
+            message(STATUS "Debug build detected - disabling matchcompiler")
+            set(USE_MATCHCOMPILER_OPT "Off")
+        endif()
+    elseif(USE_MATCHCOMPILER STREQUAL "Verify")
+        set(USE_MATCHCOMPILER_OPT "Verify")
     else()
-        set(USE_MATCHCOMPILER_OPT "Off")
+        set(USE_MATCHCOMPILER_OPT "On")
     endif()
 else()
-    set(USE_MATCHCOMPILER_OPT ${USE_MATCHCOMPILER})
+    set(USE_MATCHCOMPILER_OPT "Off")
 endif()
 
 option(BUILD_CORE_DLL       "Build lib as cppcheck-core.dll with Visual Studio"             OFF)

lib/CMakeLists.txt

@@ -10,7 +10,7 @@ function(build_src output filename)
     get_filename_component(file ${filename} NAME)
     set(outfile ${CMAKE_CURRENT_BINARY_DIR}/build/mc_${file})
     set(${output} ${${output}} ${outfile} PARENT_SCOPE)
-    if (USE_MATCHCOMPILER STREQUAL "Verify")
+    if (USE_MATCHCOMPILER_OPT STREQUAL "Verify")
         set(verify_option "--verify")
     endif()
     add_custom_command(