chore: 移除空桩文件（PassManager.cpp/ConstEval.cpp）从构建

这些文件仅含注释或include，无实际代码。

src/ir/passes/CMakeLists.txt

@@ -1,5 +1,4 @@
 add_library(ir_passes STATIC
-  PassManager.cpp
   Mem2Reg.cpp
   LICM.cpp
   ConstFold.cpp

src/mir/passes/CMakeLists.txt

@@ -1,5 +1,4 @@
 add_library(mir_passes STATIC
-  PassManager.cpp
   Peephole.cpp
   BlockLayoutOpt.cpp
   MIRCleanup.cpp

src/sem/CMakeLists.txt

@@ -1,7 +1,6 @@
 add_library(sem STATIC
   Sema.cpp
   SymbolTable.cpp
-  ConstEval.cpp
 )
 
 target_link_libraries(sem PUBLIC