CMakeAddFortranSubdirectory: Fail when the MinGW configure or build fails

The configure and build wrapper scripts ignored the result of
`execute_process`, so a failure in the MinGW project (e.g. a gfortran
compilation error) was not reported and the parent build continued,
failing later at link time or not at all.

Closes: #28240

Modules/CMakeAddFortranSubdirectory/build_mingw.cmake.in

@@ -8,4 +8,6 @@ foreach(byproduct IN LISTS byproducts)
     set(clean_first --clean-first)
   endif()
 endforeach()
-execute_process(COMMAND "@CMAKE_COMMAND@" --build . ${clean_first})
+execute_process(
+  COMMAND "@CMAKE_COMMAND@" --build . ${clean_first}
+  COMMAND_ERROR_IS_FATAL ANY)

Modules/CMakeAddFortranSubdirectory/config_mingw.cmake.in

@@ -6,4 +6,5 @@ execute_process(
   -DBUILD_SHARED_LIBS=ON
   -DCMAKE_GNUtoMS=ON
   ${CMAKE_COMMAND_LINE}
-  "@source_dir@")
+  "@source_dir@"
+  COMMAND_ERROR_IS_FATAL ANY)