bug#42091: mesa-20.0.8 fails during testing: preprocessor error: syntax error, unexpected end of file

[Thorsten Wilms]

This pattern with preprocessor error repeats several times in the log
file, this is the very end of it:

```
015-define-object-with-parens: PASS
150/151 tests returned correct results
--- stderr ---
--- 

+++ 

@@ -1,2 +1,2 @@

-0:2(8): preprocessor error: syntax error, unexpected end of file
+0:2(8): preprocessor error: syntax error, unexpected $end
 
-------

73/94 mesa:intel / anv_state_pool             FAIL     0.42 s (killed
by signal 11 SIGSEGV)

--- command ---
17:45:12 /tmp/guix-build-mesa-20.0.8.drv-0/build/src/intel/vulkan/state_pool
-------

Full log written
to /tmp/guix-build-mesa-20.0.8.drv-0/build/meson-logs/testlog.txt
FAILED:
meson-test 
/gnu/store/x7yb6fg9d4qv8d2nfqdnlih43y8d6whf-meson-for-build-0.53.2/bin/meson
test --no-rebuild --print-errorlogs ninja: build stopped: subcommand
failed. command "ninja" "test" failed with status 1
```