Fix copying of partial characters for UTF-8 input (libexpat bug 115):
https://github.com/libexpat/libexpat/issues/115

(cherry picked from commit 759e30ec)

The standard header stdbool.h is not available
with old Visual Studio compilers

Cherry-picked from libexpat b4b89c2ab0cc5325a41360c25ef9d2ccbe617e5c.

expat: Add artificial scopes in xmltok.c utf8_toUtf8() to fix c89 compilation.

Cherry-picked from libexpat commit e0b290eb3d8f4c4b45137a7d7f4f8db812145bd2