[docs][Windows] Add forgotten ^ to LLVM_TARGETS_TO_BUILD

Author: AndrewSB

docs/Windows.md

@@ -108,7 +108,7 @@ cmake -G "Ninja"^
  -DLLVM_TOOL_COMPILER_RT_BUILD=TRUE^
  -DLLVM_BUILD_EXTERNAL_COMPILER_RT=TRUE^
  -DLLVM_LIT_ARGS=-sv^
- -DLLVM_TARGETS_TO_BUILD=X86
+ -DLLVM_TARGETS_TO_BUILD=X86^
  "%swift_source_dir%/llvm"
 popd
 cmake --build "%swift_source_dir%/build/Ninja-DebugAssert/llvm-windows-amd64"