meson: use files() instead of joining paths

The Meson docs points out that it's better to use the files() function
when referring to files in the source tree than manually constructing
paths like this. Let's follow that advice, and get some neat cleanups.

Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20907>

src/compiler/glsl/glcpp/meson.build

@@ -89,7 +89,7 @@ if with_any_opengl and with_tests and meson.can_run_host_binaries() and \
       'glcpp test (@0@)'.format(m),
       prog_python,
       args : [
-        join_paths(meson.current_source_dir(), 'tests/glcpp_test.py'),
+        files('tests/glcpp_test.py'),
         glcpp, join_paths(meson.current_source_dir(), 'tests'),
         '--@0@'.format(m),
       ],

src/compiler/glsl/tests/meson.build

@@ -71,7 +71,7 @@ if meson.can_run_host_binaries()
     'glsl compiler warnings',
     prog_python,
     args : [
-      join_paths(meson.current_source_dir(), 'warnings_test.py'),
+      files('warnings_test.py'),
       '--glsl-compiler', glsl_compiler,
       '--test-directory', join_paths(
         dir_source_root, 'src', 'compiler', 'glsl', 'tests', 'warnings'
@@ -85,7 +85,7 @@ if meson.can_run_host_binaries()
     'glsl optimization',
     prog_python,
     args : [
-      join_paths(meson.current_source_dir(), 'optimization_test.py'),
+      files('optimization_test.py'),
       '--test-runner', glsl_test
     ],
     suite : ['compiler', 'glsl'],
@@ -97,14 +97,14 @@ if with_tools.contains('glsl')
     'glsl dump-builder test',
     glsl_compiler,
     args : ['--version', '110', '--dump-builder',
-            join_paths(meson.current_source_dir(), 'standalone_dump-builder.frag'),
+            files('standalone_dump-builder.frag'),
            ],
     suite : ['compiler', 'glsl'],
   )
   test(
     'glsl lower-precision test',
     prog_python,
-    args : [join_paths(meson.current_source_dir(), 'lower_precision_test.py'),
+    args : [files('lower_precision_test.py'),
             glsl_compiler
            ],
     suite : ['compiler', 'glsl'],

src/compiler/nir/meson.build

@@ -421,7 +421,7 @@ if with_tests
     'nir_algebraic_parser',
     prog_python,
     args : [
-      join_paths(meson.current_source_dir(), 'tests/algebraic_parser_test.py')
+      files('tests/algebraic_parser_test.py')
     ],
     suite : ['compiler', 'nir'],
   )