Fix ARM64 Windows build to use single-source compilation

clang/lld-link cannot link against DLL directly - it needs an import library.
Use single-source build for ARM64 to avoid this issue.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Jarred-Sumner

win32/build-tcc.bat

@@ -119,6 +119,8 @@ goto :p3
 :tarm64
 set D=%DARM64%
 set P=%PARM64%
+@rem ARM64 with clang: use single-source build (lld-link can't link DLL directly)
+set TCC_C=..\tcc.c
 goto :p3
 
 :p3