build: Fix up spirv_info.Plo

spirv_info.c existed as a static file until commit 2dd4e2ece3 began
generating it as part of the build process. autotools is incapable of
coping, and so a build-tree from before this commit would then fail with
it:

[4]: *** No rule to make target '../../../mesa/src/compiler/spirv/spirv_info.c', needed by 'spirv/spirv_info.lo'.  Stop.

Add a few lines to configure.ac to update the broken build files.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

configure.ac

@@ -2914,6 +2914,8 @@ AC_OUTPUT
 # source file
 $SED -i -e 's/brw_blorp.cpp/brw_blorp.c/' src/mesa/drivers/dri/i965/.deps/brw_blorp.Plo
 
+rm -f src/compiler/spirv/spirv_info.lo
+echo "# dummy" > src/compiler/spirv/.deps/spirv_info.Plo
 
 dnl
 dnl Output some configuration info for the user