app-text/ghostscript-gpl: fix zlib.h build error #573248

Newer versions of ghostscript refer to the zlib.h header file directly in
the makefiles.  Since we point it to a bogus place, that fails.  Change it
to an empty value since checking it for deps is pointless for our builds.

app-text/ghostscript-gpl/ghostscript-gpl-9.18.ebuild

@@ -124,6 +124,10 @@ src_prepare() {
  sed -i \
  -e "/^ZLIBDIR=/s:=.*:=${T}:" \
  configure.ac || die
+ # Some files depend on zlib.h directly. Redirect them. #573248
+ sed -i \
+ -e '/^zlib_h/s:=.*:=:' \
+ base/lib.mak || die
 
  # search path fix
  # put LDFLAGS after BINDIR, bug #383447