gallium: Avoid empty version scripts in pipe-loader

Meson produces version scripts with an empty global node for disabled
drivers. This is reported as syntax error by the linker.
The root cause of the problem is that the version scripts are
accumulated in the out of foreach `pipe_loader_link_args` variable
although they should be only used once for their driver specific loader
library.
Fixes build errors when some of the drivers are disabled like on arm64
which disables i915 due to missing dependencies.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/10166
Fixes: 667de678a0 ("gallium: Fix undefined symbols in version scripts")
Signed-off-by: Janne Grunau <j@jannau.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26268>

src/gallium/targets/pipe-loader/meson.build

@@ -80,11 +80,13 @@ foreach x : pipe_loaders
 
   pipe_sym = configure_file(input : 'pipe.sym.in', output : 'pipe_@0@.sym'.format(x[1]), configuration : pipe_sym_config)
 
+  cur_pipe_loader_link_args = pipe_loader_link_args
+  cur_pipe_loader_link_deps = pipe_loader_link_deps
   if with_ld_version_script
-    pipe_loader_link_args += [
+    cur_pipe_loader_link_args += [
       '-Wl,--version-script', join_paths(meson.current_build_dir(), 'pipe_@0@.sym'.format(x[1]))
     ]
-    pipe_loader_link_deps += pipe_sym
+    cur_pipe_loader_link_deps += pipe_sym
   endif
 
   if x[0]
@@ -94,8 +96,8 @@ foreach x : pipe_loaders
       c_args : [pipe_loader_comp_args, '-DPIPE_LOADER_DYNAMIC=1'],
       cpp_args : [pipe_loader_comp_args],
       gnu_symbol_visibility : 'hidden',
-      link_args : pipe_loader_link_args,
-      link_depends : pipe_loader_link_deps,
+      link_args : cur_pipe_loader_link_args,
+      link_depends : cur_pipe_loader_link_deps,
       include_directories : pipe_loader_incs,
       link_with : [pipe_loader_link_with, x[3]],
       dependencies : [idep_mesautil, idep_nir, dep_thread, x[2]],