nir/tests: Refactor creation of loops for loop_analyze test cases

Inspired heavily by the work by Yevhenii Kolesnikov in the original
versions of !3445.

v2: Pass parameters to loop_builder using a struct. Add a comment
describing the loop being constructed to loop_builder. Both suggested by
Caio.

v3: mscv C++ designated initializer lolz.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21289>

src/compiler/nir/meson.build

@@ -392,6 +392,12 @@ idep_nir = declare_dependency(
 )
 
 if with_tests
+  if cc.get_id() == 'msvc' and cc.version().version_compare('< 19.29')
+    msvc_designated_initializer = 'cpp_std=c++latest'
+  else
+    msvc_designated_initializer = 'cpp_std=c++20'
+  endif
+
   test(
     'nir_tests',
     executable(
@@ -413,6 +419,7 @@ if with_tests
         'tests/vars_tests.cpp',
       ),
       cpp_args : [cpp_msvc_compat_args],
+      override_options: [msvc_designated_initializer],
       gnu_symbol_visibility : 'hidden',
       include_directories : [inc_include, inc_src, inc_mapi, inc_mesa, inc_gallium, inc_gallium_aux],
       dependencies : [dep_thread, idep_gtest, idep_nir, idep_mesautil],