[S390x] Fix endian bug in minipal

[saitama951]

after #107889 is merged we see test cases crashing on s390x

Starting program: /home/sanjam/test-build-script/build-scripts-s390x/runtime/runtime/.dotnet/dotnet --info
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x3fff63008c0 (LWP 1186966)]
[New Thread 0x3fff45008c0 (LWP 1186967)]
[New Thread 0x3fff42008c0 (LWP 1186968)]
Process terminated.
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Thread 1 "dotnet" received signal SIGABRT, Aborted.
__pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
44            return INTERNAL_SYSCALL_ERROR_P (ret) ? INTERNAL_SYSCALL_ERRNO (ret) : 0;

This is primarily because the "BIGENDIAN" macro is defined in src/native/minipal/minipalconfig.h.in which generates a minipalconfig.h which needs to be included in utf8.c in order for the macro to be used there.

[saitama951]

cc: @jkoritzinsky

[saitama951]

can this be merged?