chore(build): viperc 路径集中为 VIPERC 常量并切换 vpcbuild3

- BuildKernel / BuildLibs / BuildApps 共用 VIPERC，去掉三处硬编码
- 指向 ViperC/__vpcbuild3__/output/viperc.exe

build.py

@@ -4,6 +4,12 @@ import sys
 import subprocess
 
 
+# ============================================================================
+# viperc 编译器路径 —— 唯一来源，改这里即可
+# ============================================================================
+VIPERC = r'..\..\ViperC\__vpcbuild3__\output\viperc.exe'
+
+
 # 解析参数
 clean = '--noclean' not in sys.argv
 kernel_only = '--kernel-only' in sys.argv
@@ -41,7 +47,7 @@ if kernel_only and nokernel:
 
 def BuildKernel():
     """编译内核：链接器一次产出带符号 kernel.elf，再由 objcopy 二次处理成裸镜像 kernel.bin"""
-    cmd = r'..\..\ViperC\__vpcbuild__\output\viperc.exe --project ./VKernel/project.vpj --clear-cache --rebuild-includes'
+    cmd = rf'{VIPERC} --project ./VKernel/project.vpj --clear-cache --rebuild-includes'
     if clean:
         cmd += ' --clean'
     os.system(cmd)
@@ -78,7 +84,7 @@ def BuildLibs():
     """编译 Libs/ 下的动态库（应用运行期经 LOAD_SO 加载）。"""
     os.makedirs("./disk/libs", exist_ok=True)
     for proj, out in LIB_LIST:
-        cmd = rf'..\..\ViperC\__vpcbuild__\output\viperc.exe --project {proj}/project.vpj --clear-cache'
+        cmd = rf'{VIPERC} --project {proj}/project.vpj --clear-cache'
         if clean:
             cmd += ' --clean'
         os.system(cmd)
@@ -123,7 +129,7 @@ def BuildApps():
     for name, proj, out, dst in APP_LIST:
         if app_filter is not None and name not in app_filter:
             continue
-        cmd = rf'..\..\ViperC\__vpcbuild__\output\viperc.exe --project {proj}/project.vpj --clear-cache'
+        cmd = rf'{VIPERC} --project {proj}/project.vpj --clear-cache'
         if clean:
             cmd += ' --clean'
         os.system(cmd)