Statically compile libstdc++ everywhere if asked

PR #93918 made it so that `-static-libstdc++` was only set in one place,
and was only set during linking, but accidentally also made it so that
it is no longer passed when building LLD or sanitizers, only when
building LLVM itself. This moves the logic for setting
`-static-libstdc++` in the linker flags back to `configure_cmake` so
that it takes effect for all CMake invocations in `native.rs`.

As a side-effect, this also causes libstdc++ to be statically compiled
into sanitizers and LLD if `llvm-tools-enabled` is set but
`llvm-static-stdcpp` is not, even though previously it was only linked
statically if `llvm-static-stdcpp` was set explicitly. But that seems
more like the expected behavior anyway.

Author: Jon Gjengset

src/bootstrap/native.rs

@@ -259,18 +259,6 @@ impl Step for Llvm {
             cfg.define("LLVM_LINK_LLVM_DYLIB", "ON");
         }
 
-        // For distribution we want the LLVM tools to be *statically* linked to libstdc++.
-        // We also do this if the user explicitly requested static libstdc++.
-        if builder.config.llvm_tools_enabled || builder.config.llvm_static_stdcpp {
-            if !target.contains("msvc") && !target.contains("netbsd") {
-                if target.contains("apple") {
-                    ldflags.push_all("-static-libstdc++");
-                } else {
-                    ldflags.push_all("-Wl,-Bsymbolic -static-libstdc++");
-                }
-            }
-        }
-
         if target.starts_with("riscv") && !target.contains("freebsd") {
             // RISC-V GCC erroneously requires linking against
             // `libatomic` when using 1-byte and 2-byte C++
@@ -576,6 +564,18 @@ fn configure_cmake(
         ldflags.push_all(&flags);
     }
 
+    // For distribution we want the LLVM tools to be *statically* linked to libstdc++.
+    // We also do this if the user explicitly requested static libstdc++.
+    if builder.config.llvm_tools_enabled || builder.config.llvm_static_stdcpp {
+        if !target.contains("msvc") && !target.contains("netbsd") {
+            if target.contains("apple") {
+                ldflags.push_all("-static-libstdc++");
+            } else {
+                ldflags.push_all("-Wl,-Bsymbolic -static-libstdc++");
+            }
+        }
+    }
+
     cfg.define("CMAKE_SHARED_LINKER_FLAGS", &ldflags.shared);
     cfg.define("CMAKE_MODULE_LINKER_FLAGS", &ldflags.module);
     cfg.define("CMAKE_EXE_LINKER_FLAGS", &ldflags.exe);