Revert "[CMake] Never force RUN_SERIAL in roottest when using Ninja"

This reverts commit c8d6ef5, again:
The same change was already attempted in commit e8519e4 ("[roottest]
Remove sequential compilation with Ninja.") and reverted in bab6bef
which also holds some explanations and pointers why Ninja cannot be
launched concurrently.

Author: hahnjo

cmake/modules/RootMacros.cmake

@@ -2367,6 +2367,9 @@ macro(ROOTTEST_COMPILE_MACRO filename)
     set_property(TEST ${COMPILE_MACRO_TEST} PROPERTY FAIL_REGULAR_EXPRESSION "Warning in")
   endif()
   set_property(TEST ${COMPILE_MACRO_TEST} PROPERTY ENVIRONMENT ${ROOTTEST_ENVIRONMENT})
+  if(CMAKE_GENERATOR MATCHES Ninja AND NOT MSVC)
+    set_property(TEST ${COMPILE_MACRO_TEST} PROPERTY RUN_SERIAL true)
+  endif()
   if (ARG_FIXTURES_SETUP)
     set_property(TEST ${COMPILE_MACRO_TEST} PROPERTY
       FIXTURES_SETUP ${ARG_FIXTURES_SETUP})
@@ -2469,6 +2472,9 @@ macro(ROOTTEST_GENERATE_DICTIONARY dictname)
                                     -- ${always-make})
 
   set_property(TEST ${GENERATE_DICTIONARY_TEST} PROPERTY ENVIRONMENT ${ROOTTEST_ENVIRONMENT})
+  if(CMAKE_GENERATOR MATCHES Ninja AND NOT MSVC)
+    set_property(TEST ${GENERATE_DICTIONARY_TEST} PROPERTY RUN_SERIAL true)
+  endif()
 
   if (ARG_FIXTURES_SETUP)
     set_property(TEST ${GENERATE_DICTIONARY_TEST} PROPERTY
@@ -2582,6 +2588,9 @@ macro(ROOTTEST_GENERATE_REFLEX_DICTIONARY dictionary)
                                     -- ${always-make})
 
   set_property(TEST ${GENERATE_REFLEX_TEST} PROPERTY ENVIRONMENT ${ROOTTEST_ENVIRONMENT})
+  if(CMAKE_GENERATOR MATCHES Ninja AND NOT MSVC)
+    set_property(TEST ${GENERATE_REFLEX_TEST} PROPERTY RUN_SERIAL true)
+  endif()
 
   if (ARG_FIXTURES_SETUP)
     set_property(TEST ${GENERATE_REFLEX_TEST} PROPERTY
@@ -2702,6 +2711,10 @@ macro(ROOTTEST_GENERATE_EXECUTABLE executable)
       RESOURCE_LOCK ${ARG_RESOURCE_LOCK})
   endif()
 
+  if(CMAKE_GENERATOR MATCHES Ninja AND NOT MSVC)
+    set_property(TEST ${GENERATE_EXECUTABLE_TEST} PROPERTY RUN_SERIAL true)
+  endif()
+
   if(MSVC AND NOT CMAKE_GENERATOR MATCHES Ninja)
     add_custom_command(TARGET ${executable} POST_BUILD
        COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/${executable}.exe