spice: convert to meson

Faster compilation.

Removed autotools patches.

Backported meson patch to fix compilation and pkgconfig file.

Before:

time make package/spice/compile -j 12
Executed in   62.85 secs   fish           external
   usr time   56.45 secs  276.00 micros   56.45 secs
   sys time    8.06 secs   46.00 micros    8.06 secs

Before + PKG_BUILD_PARALLEL:

Executed in   45.40 secs   fish           external
   usr time   63.08 secs  253.00 micros   63.08 secs
   sys time    8.57 secs   44.00 micros    8.57 secs

After:

time make package/spice/compile -j 12
Executed in   16.54 secs   fish           external
   usr time   41.29 secs  266.00 micros   41.29 secs
   sys time    4.76 secs   45.00 micros    4.76 secs

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/spice/patches/010-librt-libm.patch

@@ -0,0 +1,28 @@
+From 26bbb85c150f882c05399e4c574208b8b1242082 Mon Sep 17 00:00:00 2001
+From: James Le Cuirot <chewi@gentoo.org>
+Date: Tue, 7 Apr 2020 19:32:15 +0100
+Subject: [PATCH] build: Fix librt and libm dependencies in Meson
+
+They need to be requested without the lib prefix, otherwise a
+generated pkg-config file ends up with absolute paths instead of -l
+flags.
+
+Signed-off-by: James Le Cuirot <chewi@gentoo.org>
+Acked-by: Frediano Ziglio <fziglio@redhat.com>
+---
+ meson.build | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/meson.build b/meson.build
+index 1685c077..f9090a82 100644
+--- a/meson.build
++++ b/meson.build
+@@ -102,7 +102,7 @@ foreach dep : ['libjpeg', 'zlib']
+ endforeach
+ 
+ if host_machine.system() != 'windows'
+-  foreach dep : ['librt', 'libm']
++  foreach dep : ['rt', 'm']
+     spice_server_deps += compiler.find_library(dep)
+   endforeach
+ else