ci: Build d3d12 gallium driver in debian-x86_32

Adding d3d12 to this ci build will prevent issues such
as #6708 or fixes like !26363 from happening again in the future.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26447>

meson.build

@@ -1048,6 +1048,7 @@ else
     '-fno-trapping-math',
     '-Qunused-arguments',
     '-fno-common',
+    '-Wno-unknown-pragmas',
     # Clang
     '-Wno-microsoft-enum-value',
     '-Wno-unused-function',
@@ -1067,6 +1068,7 @@ else
     # to the memory before the constructor as "dead stores".
     # For now we disable this optimization.
     '-flifetime-dse=1',
+    '-Wno-unknown-pragmas',
     # Clang
     '-Wno-microsoft-enum-value',
   ]