meson: cups: use cups-config for looking up cups

We were looking for the cups headers and the cups lib in the default locations
which for example breaks with OpenBSD where the cups headers are under /usr/local/include/

Instead just use the "cups" dependency type from meson which internally uses cups-config.

Fixes #1967

modules/printbackends/meson.build

@@ -69,38 +69,21 @@ if enabled_print_backends.contains('cloudprint')
 endif
 
 if enabled_print_backends.contains('cups')
-  cups_error = ''
-  if cc.has_header('cups/cups.h')
-    cups_major_version = cc.compute_int('CUPS_VERSION_MAJOR', prefix : '#include <cups/cups.h>')
-    cups_minor_version = cc.compute_int('CUPS_VERSION_MINOR', prefix : '#include <cups/cups.h>')
-    cups_version = '@0@.@1@'.format(cups_major_version, cups_minor_version)
-    message('Found CUPS version: @0@'.format(cups_version))
-    if cups_version.version_compare('<1.7')
-      cups_error = 'Need CUPS version >= 1.7'
-    else
-      libcups = cc.find_library('cups', required : true)
-    endif
-  else
-    cups_error = 'Cannot find CUPS headers in default prefix.'
-  endif
+  cups_dep = dependency('cups', version : '>=1.7', required: print_strict_deps)
+  if cups_dep.found()
+    cups_extra_deps = []
 
-  cups_extra_deps = []
-  enable_colord = get_option('colord')
-  if enable_colord != 'no'
-    want_colord = enable_colord == 'yes'
-    colord_dep = dependency('colord', version: '>= 0.1.9', required: want_colord)
-    cdata.set('HAVE_COLORD', colord_dep.found() ? 1 : false)
-    cups_extra_deps += [colord_dep]
-  endif
-
-  if cups_error != ''
-    if print_strict_deps
-      error(cups_error)
-    else
-      message(cups_error)
+    enable_colord = get_option('colord')
+    if enable_colord != 'no'
+      want_colord = enable_colord == 'yes'
+      colord_dep = dependency('colord', version: '>= 0.1.9', required: want_colord)
+      cdata.set('HAVE_COLORD', colord_dep.found() ? 1 : false)
+      cups_extra_deps += [colord_dep]
     endif
-  else
+
     print_backends += ['cups']
+  else
+    message('\'cups\' backend disabled: missing dependencies')
   endif
 endif
 
@@ -168,7 +151,7 @@ if print_backends.contains('cups')
                 'cups/gtkcupsutils.c',
                 'cups/gtkcupssecretsutils.c',
                 c_args: printbackends_args,
-                dependencies: [libgtk_dep, libcups] + cups_extra_deps,
+                dependencies: [libgtk_dep, cups_dep] + cups_extra_deps,
                 install_dir: printbackends_install_dir,
                 install : true)
 endif