beam_load.c: Add overflow check of tag values

The handling of large values for other tags than TAG_i (integer) is
buggy.  Any tag value equal to or greater than 2^40 (5 bytes) will
abort loading.  Tag values fitting in 5 bytes will be truncated to 4
bytes values.

Those bugs cause real problems because the bs_init2/6 and
bs_init_bits/6 instructions unfortunately use TAG_u to encode literal
sizes (using TAG_i would have been a better choice, but it is too late
to change that now).  Any binary size that cannot fit in an Uint
should cause a system_limit exception at run-time, but instead the
buggy handling will either cause an emulator crash (for values in the
range 2^32 to 2^40-1) or abort loading.

In this commit, implement overflow checking of tag values as a
preparation for fixing the binary construction instructions.  If any
tag value cannot fit in an Uint (except for TAG_i), change the
tag to the special TAG_o overflow tag.

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