debian/changelog

+mesa (18.3.4-2) UNRELEASED; urgency=medium
+
+  * Cherry-pick f6556ec7d12 (dri: meson: do not prefix user provided dri-
+    drivers-path) from upstream master branch. Fixes a regression since
+    switching to meson (Closes: #922807).
+
+ -- Andreas Boll <aboll@debian.org>  Thu, 28 Feb 2019 11:45:35 +0100
+
 mesa (18.3.4-1) unstable; urgency=medium
 
   * New upstream release.

meson.build

@@ -64,11 +64,11 @@ endif
 
 dri_drivers_path = get_option('dri-drivers-path')
 if dri_drivers_path == ''
-  dri_drivers_path = join_paths(get_option('libdir'), 'dri')
+  dri_drivers_path = join_paths(get_option('prefix'), get_option('libdir'), 'dri')
 endif
 dri_search_path = get_option('dri-search-path')
 if dri_search_path == ''
-  dri_search_path = join_paths(get_option('prefix'), dri_drivers_path)
+  dri_search_path = dri_drivers_path
 endif
 
 with_gles1 = get_option('gles1')

src/mesa/drivers/dri/meson.build

@@ -78,7 +78,7 @@ if with_dri
     filebase : 'dri',
     description : 'Direct Rendering Infrastructure',
     version : meson.project_version(),
-    variables : ['dridriverdir=${prefix}/' + dri_drivers_path],
+    variables : ['dridriverdir=' + dri_drivers_path],
     requires_private : dri_req_private,
   )
 endif