gnu: mupdf: Use only dynamic linking.

* gnu/packages/pdf.scm (mupdf)[source]: Add patch.
[arguments]: Build and find the shared library.
(zathura-pdf-mupdf)[arguments]: Add a 'remove-libmupdfthird.a-requirement
phase to deal with the now-missing static one.
* gnu/packages/patches/mupdf-fix-linkage.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -1367,6 +1367,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/mumps-shared-libseq.patch		\
   %D%/packages/patches/mumps-shared-mumps.patch			\
   %D%/packages/patches/mumps-shared-pord.patch			\
+  %D%/packages/patches/mupdf-fix-linkage.patch			\
   %D%/packages/patches/mupen64plus-ui-console-notice.patch	\
   %D%/packages/patches/mupen64plus-video-z64-glew-correct-path.patch    \
   %D%/packages/patches/musl-cross-locale.patch			\

gnu/packages/patches/mupdf-fix-linkage.patch

@@ -0,0 +1,27 @@
+From: Tobias Geerinckx-Rice <me@tobias.gr>
+Date: Tue, 24 Nov 2020 10:29:28 +0000
+Subject: [PATCH] gnu: mupdf: Fix linkage.
+
+Replace broken linkage to ‘build/shared-release/libmupdf.so’ with the
+proper ‘-L$(libdir) -lmupdf’ incantation, and fix libmupdf.so's mode.
+
+--- mupdf-1.18.0-source.org/Makefile
++++ mupdf-1.18.0-source/Makefile
+@@ -61,7 +61,7 @@
+ ifdef RANLIB
+   RANLIB_CMD = $(QUIET_RANLIB) $(RANLIB) $@
+ endif
+-LINK_CMD = $(QUIET_LINK) $(MKTGTDIR) ; $(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
++LINK_CMD = $(QUIET_LINK) $(MKTGTDIR) ; $(CC) $(LDFLAGS) -o $@ $(subst $(MUPDF_LIB),-L$(libdir) -L$(OUT) -lmupdf,$^) $(LIBS)
+ TAGS_CMD = $(QUIET_TAGS) ctags -R --c-kinds=+p
+ WINDRES_CMD = $(QUIET_WINDRES) $(MKTGTDIR) ; $(WINDRES) $< $@
+ OBJCOPY_CMD = $(QUIET_OBJCOPY) $(MKTGTDIR) ; $(LD) -r -b binary -z noexecstack -o $@ $<
+@@ -364,7 +364,7 @@ install: libs apps
+ 	install -m 644 include/mupdf/pdf/*.h $(DESTDIR)$(incdir)/mupdf/pdf
+ 
+ 	install -d $(DESTDIR)$(libdir)
+-	install -m 644 $(INSTALL_LIBS) $(DESTDIR)$(libdir)
++	install -m 755 $(INSTALL_LIBS) $(DESTDIR)$(libdir)
+ 
+ 	install -d $(DESTDIR)$(bindir)
+ 	install -m 755 $(TOOL_APPS) $(VIEW_APPS) $(DESTDIR)$(bindir)

gnu/packages/pdf.scm

@@ -526,6 +526,12 @@ using the DjVuLibre library.")
                                "-Dlink-external=true")
        #:phases
        (modify-phases %standard-phases
+         (add-after 'unpack 'remove-libmupdfthird.a-requirement
+           (lambda _
+             ;; Ignore a missing (apparently superfluous) static library.
+             (substitute* "meson.build"
+               ((".*mupdfthird.*") ""))
+             #t))
          (add-before 'configure 'add-mujs-to-dependencies
            (lambda _
              ;; Add mujs to the 'build_dependencies'.
@@ -692,6 +698,7 @@ extracting content or merging files.")
                            "mupdf-" version "-source.tar.xz"))
        (sha256
         (base32 "16m5sksil22sshxy70xkslsb2qhvcqb1d95i9savnhds1xn4ybar"))
+       (patches (search-patches "mupdf-fix-linkage.patch"))
        (modules '((guix build utils)))
        (snippet
         '(begin
@@ -730,6 +737,10 @@ extracting content or merging files.")
                            "XCFLAGS=-fpic"
                            "USE_SYSTEM_LIBS=yes"
                            "USE_SYSTEM_MUJS=yes"
+                           "shared=yes"
+                           ;; Even with the linkage patch we must fix RUNPATH.
+                           (string-append "LDFLAGS=-Wl,-rpath="
+                                          (assoc-ref %outputs "out") "/lib")
                            (string-append "prefix=" (assoc-ref %outputs "out")))
         #:phases (modify-phases %standard-phases
                    (delete 'configure)))) ; no configure script