Bug#972736: Mesa 20.2.1 fails to build on x32 (debian\rules issue)

[Stuart Young <cefiar@gmail.com>]

Patch for debian/rules attached to resolve this bug.

Note: By just checking if the variable is empty first, the patch is non-specific to x32. It covers the x32 build issue, but will also avoid such issues for any platform that AMD vulkan drivers aren't built on, but that can support intel vulkan drivers.

--

Stuart Young (aka Cefiar)

--- a/debian/rules	2020-11-03 15:11:24.262177791 +1100
+++ b/debian/rules	2020-11-03 15:20:36.960909848 +1100
@@ -75,7 +75,12 @@
 		GALLIUM_DRIVERS += ,svga,zink
 		# svga needs xa state tracker
 		confflags_GALLIUM += -Dgallium-xa=true
-		VULKAN_DRIVERS += ,intel
+		# VULKAN_DRIVERS var may be empty
+		ifeq ($(strip $(VULKAN_DRIVERS)),)
+			VULKAN_DRIVERS = intel
+		else
+			VULKAN_DRIVERS += ,intel
+		endif
 	endif
 
 	# Non-Linux ports also lack *_CLOEXEC and epoll, so wayland isn't ready yet: