Log Message:
Update print/mupdf to 1.8.

pkgsrc changes:
 * Bump BUILDLINK_API_DEPENDS (spotted and tested via the only print/mupdf
   consumer wip/zathura-mupdf)
 * OpenGL-based desktop viewer is still not enabled by default neither upstream
   nor in pkgsrc

Changes:
List of changes in MuPDF 1.8
* Headline changes:
	* New OpenGL-based barebones desktop viewer.
	* New URW fonts with greek and cyrillic.
	* 64-bit file support.
	* Ghostscript proofing mode (source only; not in shipped binaries).
* EPUB improvements:
	* User style sheets.
	* GIF images (also for CBZ).
	* Table of contents.
	* CJK text.
	* Page margins.
	* Many bug fixes.
* Bug fixes:
	* Updated FreeType to version 2.6.1.
	* Various font substitution bug fixes.
	* Fix setjmp/longjmp behaviour which could cause optimizing compilers to misbehave.