In pTk/mTk/generic/tkCanvText.c, the declaration of "length" at line 1237 needs to be changed from:

int length;
to:
size_t length;
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This change is already in place in the source of Tk-804.036 that I've been using.
I don't know why that's not the case with the source you are using.

Cheers,
Rob