meson: simplify install_megadrivers.py invocation

Note: `find_program()` needs a shebang on scripts.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
diff --git a/bin/install_megadrivers.py b/bin/install_megadrivers.py
index 470137e..0a28dd7 100644
--- a/bin/install_megadrivers.py
+++ b/bin/install_megadrivers.py
@@ -1,5 +1,6 @@
+#!/usr/bin/env python3
 # encoding=utf-8
-# Copyright © 2017-2018 Intel Corporation
+# Copyright 2017-2018 Intel Corporation
 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
diff --git a/bin/meson.build b/bin/meson.build
index ec22e2e..000abef 100644
--- a/bin/meson.build
+++ b/bin/meson.build
@@ -20,3 +20,4 @@
 
 git_sha1_gen_py = files('git_sha1_gen.py')
 symbols_check = find_program('symbols-check.py')
+install_megadrivers_py = find_program('install_megadrivers.py')
diff --git a/src/gallium/targets/dri/meson.build b/src/gallium/targets/dri/meson.build
index f4645cf..954b218 100644
--- a/src/gallium/targets/dri/meson.build
+++ b/src/gallium/targets/dri/meson.build
@@ -110,8 +110,7 @@
 endforeach
 
 meson.add_install_script(
-  prog_python.path(),
-  join_paths(meson.source_root(), 'bin/install_megadrivers.py'),
+  install_megadrivers_py.path(),
   libgallium_dri.full_path(),
   dri_drivers_path,
   gallium_dri_drivers,
diff --git a/src/gallium/targets/va/meson.build b/src/gallium/targets/va/meson.build
index 3cf6820..24d291c 100644
--- a/src/gallium/targets/va/meson.build
+++ b/src/gallium/targets/va/meson.build
@@ -65,8 +65,7 @@
 endforeach
 
 meson.add_install_script(
-  prog_python.path(),
-  join_paths(meson.source_root(), 'bin/install_megadrivers.py'),
+  install_megadrivers_py.path(),
   libva_gallium.full_path(),
   va_drivers_path,
   va_drivers,
diff --git a/src/gallium/targets/vdpau/meson.build b/src/gallium/targets/vdpau/meson.build
index 155d500..2032fa0 100644
--- a/src/gallium/targets/vdpau/meson.build
+++ b/src/gallium/targets/vdpau/meson.build
@@ -71,8 +71,7 @@
 endforeach
 
 meson.add_install_script(
-  prog_python.path(),
-  join_paths(meson.source_root(), 'bin/install_megadrivers.py'),
+  install_megadrivers_py.path(),
   libvdpau_gallium.full_path(),
   vdpau_drivers_path,
   vdpau_drivers,
diff --git a/src/gallium/targets/xvmc/meson.build b/src/gallium/targets/xvmc/meson.build
index c107104..c1f2019 100644
--- a/src/gallium/targets/xvmc/meson.build
+++ b/src/gallium/targets/xvmc/meson.build
@@ -60,8 +60,7 @@
 endforeach
 
 meson.add_install_script(
-  prog_python.path(),
-  join_paths(meson.source_root(), 'bin/install_megadrivers.py'),
+  install_megadrivers_py.path(),
   libxvmc_gallium.full_path(),
   xvmc_drivers_path,
   xvmc_drivers,
diff --git a/src/mesa/drivers/dri/meson.build b/src/mesa/drivers/dri/meson.build
index 1614744..acf7d2e 100644
--- a/src/mesa/drivers/dri/meson.build
+++ b/src/mesa/drivers/dri/meson.build
@@ -74,8 +74,7 @@
   )
 
   meson.add_install_script(
-    prog_python.path(),
-    join_paths(meson.source_root(), 'bin/install_megadrivers.py'),
+    install_megadrivers_py.path(),
     libmesa_dri_drivers.full_path(),
     dri_drivers_path,
     _dri_link,