Revert "rust: recursively pull proc-macro dependencies as well"

This reverts commit aee941559c.

The commit being reverted breaks compilation of a major Meson consumer
(Mesa). As a result, various distros are either pinning to <1.4.0 (before
the commit) or performing this same revert downstream.

Fixing a regression takes priority, so let's revert.

Fixes: https://github.com/mesonbuild/meson/issues/12973

mesonbuild/build.py

@@ -1292,6 +1292,8 @@ class BuildTarget(Target):
         for t in self.link_targets:
             if t in result:
                 continue
+            if t.rust_crate_type == 'proc-macro':
+                continue
             if include_internals or not t.is_internal():
                 result.add(t)
             if isinstance(t, StaticLibrary):

test cases/rust/18 proc-macro/lib.rs

@@ -1,8 +0,0 @@
-extern crate proc_macro_examples;
-use proc_macro_examples::make_answer;
-
-make_answer!();
-
-pub fn func() -> u32 {
-    answer()
-}

test cases/rust/18 proc-macro/meson.build

@@ -31,14 +31,3 @@ main = executable(
 )
 
 test('main_test2', main)
-
-subdir('subdir')
-
-staticlib = static_library('staticlib', 'lib.rs',
-  link_with: pm_in_subdir,
-  rust_dependency_map : {'proc_macro_examples3' : 'proc_macro_examples'}
-)
-
-executable('transitive-proc-macro', 'transitive-proc-macro.rs',
-  link_with: staticlib,
-)

test cases/rust/18 proc-macro/subdir/meson.build

@@ -1 +0,0 @@
-pm_in_subdir = rust.proc_macro('proc_macro_examples3', '../proc.rs')

test cases/rust/18 proc-macro/transitive-proc-macro.rs

@@ -1,7 +0,0 @@
-extern crate staticlib;
-use staticlib::func;
-
-
-fn main() {
-    assert_eq!(42, func());
-}