build_llvm_package.bat: Build teh clang-format plugin separately
build_llvm_package.bat: Build teh clang-format plugin separately

In r293373 we switched the build to linking dynamically against the
Universal CRT and include the redistributables in the installer.

However, clang-format.exe is copied into the vsix and needs to be
statically linked. This commit makes us build the plugin in a separate
step that uses static linking.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@294513 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm