refactor: replace SPC_LIBC with SPC_TARGET and update related logic

src/SPC/util/toolchain/GccNativeToolchain.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SPC\util\toolchain;
+
+use SPC\builder\freebsd\SystemUtil as FreeBSDSystemUtil;
+use SPC\builder\linux\SystemUtil as LinuxSystemUtil;
+use SPC\builder\macos\SystemUtil as MacOSSystemUtil;
+use SPC\util\GlobalEnvManager;
+
+class GccNativeToolchain implements ToolchainInterface
+{
+    public function initEnv(string $target): void
+    {
+        GlobalEnvManager::putenv('SPC_LINUX_DEFAULT_CC=gcc');
+        GlobalEnvManager::putenv('SPC_LINUX_DEFAULT_CXX=g++');
+        GlobalEnvManager::putenv('SPC_LINUX_DEFAULT_AR=ar');
+        GlobalEnvManager::putenv('SPC_LINUX_DEFAULT_LD=ld.gold');
+    }
+
+    public function afterInit(string $target): void
+    {
+        // check gcc exists
+        match (PHP_OS_FAMILY) {
+            'Linux' => LinuxSystemUtil::findCommand('g++') ?? throw new \RuntimeException('g++ not found, please install it or set CC/CXX to a valid path.'),
+            'Darwin' => MacOSSystemUtil::findCommand('g++') ?? throw new \RuntimeException('g++ not found, please install it or set CC/CXX to a valid path.'),
+            'BSD' => FreeBSDSystemUtil::findCommand('g++') ?? throw new \RuntimeException('g++ not found, please install it or set CC/CXX to a valid path.'),
+            default => throw new \RuntimeException('GCC is not supported on ' . PHP_OS_FAMILY . '.'),
+        };
+    }
+}