Patches provided by Mathias Drochner and modified by me. This fixes PR 46698.
Changes:
* xetex.ch: XeTeX uses 256 math font families.
* XeTeX_ext.c, pdfimage.cpp, am/xetex.am: Always use poppler.
Changes:
* xetex.ch (pack_buffered_name): Adapt to modified ../tex.ch.
(read_font_info): Cast print_c_string() arg to string.
* xetex.ch: Reformulate to not depend on eTeX_version_string.
* XeTeXFontInst.h: Fix prototype for xmalloc().
* XeTeXFontMgr_FC.cpp, XeTeX_ext.c: Move (nested) extern
declaration of gFreeTypeLibrary from here ...
* XeTeX_ext.h: ... to here.
* XeTeXOTLayoutEngine.{cpp,h}: Drop support for ICU < 4.2.