Fix undefined behaviour caused by shifting (unsigned char) << 24.

Reported by Tim Sweet <tsweet64@protonmail.com>
at <https://savannah.gnu.org/bugs/?66289>.

* lib/ucs4.h (ucs4_mbtowc): Cast 'unsigned char' values to ucs4_t before
shifting them to the left.
* lib/ucs4be.h (ucs4be_mbtowc): Likewise.
* lib/ucs4le.h (ucs4le_mbtowc): Likewise.
* lib/utf32.h (utf32_mbtowc): Likewise.
* lib/utf32be.h (utf32be_mbtowc): Likewise.
* lib/utf32le.h (utf32le_mbtowc): Likewise.
7 files changed