refactor(build): linker.cmd 由绝对路径改为裸名，--asan 提示文案去硬编码

- project.vpj / repl.vpj 的 linker.cmd 改为 clang++.exe，交由 PATH 解析

- main.vp 的 --asan 运行库提示改用占位符路径，并说明 clang64 根目录由 PATH 自动探测

App/main.vp

@@ -389,9 +389,9 @@ Target: %s
     # --asan requires the project to declare the ASan runtime in project.vpj linker.static_libs (no hardcoded paths); missing fails fast
     if BuildPipeline._asan_mode != 0 and Config.asan_runtime_declared() == 0:
         log.error("Enabling --asan requires declaring the ASan runtime in project.vpj's linker.static_libs:", "asan")
-        log.error("    D:/msys64/clang64/lib/clang/22/lib/windows/libclang_rt.asan_dynamic-x86_64.dll.a", "asan")
-        log.error("    D:/msys64/clang64/lib/clang/22/lib/windows/libclang_rt.asan_dynamic_runtime_thunk-x86_64.a", "asan")
-        log.error("At runtime D:/msys64/clang64/bin (libclang_rt.asan_dynamic-x86_64.dll) must also be on PATH", "asan")
+        log.error("    <MSYS2>/clang64/lib/clang/<ver>/lib/windows/libclang_rt.asan_dynamic-x86_64.dll.a", "asan")
+        log.error("    <MSYS2>/clang64/lib/clang/<ver>/lib/windows/libclang_rt.asan_dynamic_runtime_thunk-x86_64.a", "asan")
+        log.error("The clang64 root is auto-detected from PATH (see README section 8.1)", "asan")
         return 1
 
     # === --clean: remove temp, output and includes.binary directories ===

project.vpj

@@ -13,7 +13,7 @@
         ]
     },
     "linker": {
-        "cmd": "D:/msys64/mingw64/bin/clang++.exe",
+        "cmd": "clang++.exe",
         "flags": [
             "-fuse-ld=lld",
             "-lmsvcrt",

repl.vpj

@@ -12,7 +12,7 @@
         ]
     },
     "linker": {
-        "cmd": "D:/msys64/mingw64/bin/clang++.exe",
+        "cmd": "clang++.exe",
         "flags": [
             "-fuse-ld=lld",
             "-lmsvcrt",