meson: use dependency() to find libjpeg

Prefer pkg-config to find_library because some installations of libjpeg
may place it outside the default search path.

Reported-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/meson.build b/meson.build
index 5062407..360623e 100644
--- a/meson.build
+++ b/meson.build
@@ -654,9 +654,8 @@
   vnc = declare_dependency() # dummy dependency
   png = dependency('libpng', required: get_option('vnc_png'),
                    method: 'pkg-config', static: enable_static)
-  jpeg = cc.find_library('jpeg', has_headers: ['jpeglib.h'],
-                         required: get_option('vnc_jpeg'),
-                         static: enable_static)
+  jpeg = dependency('libjpeg', required: get_option('vnc_jpeg'),
+                    method: 'pkg-config', static: enable_static)
   sasl = cc.find_library('sasl2', has_headers: ['sasl/sasl.h'],
                          required: get_option('vnc_sasl'),
                          static: enable_static)