[gn build] Port rest of 9cfeba5b (LowLevelType->Support)

This adds all the CodeGen deps all over the place.

I ran

    git show 9cfeba5b > foo2.txt

to get the original patch into a text file and then ran

    #!/usr/bin/env python3
    import os
    in_cmake = False
    for l in open('foo2.txt'):
      if l.startswith('+++ b/'):
        cmake = l[len('+++ b/'):-1]
        in_cmake = 'CMakeLists.txt' in cmake
      if not in_cmake:
        continue
      prefix = 'llvm/utils/gn/secondary/'
      gn_file = os.path.join(prefix, os.path.dirname(cmake), 'BUILD.gn')
      if l.startswith('+ '):
        add = l[1:].strip()
        if add == 'CodeGen':
          try:
            with open(gn_file) as f:
                contents = f.read()
          except:
            print(f'skipping {gn_file}')
            continue
          contents = contents.replace(' deps = [', ' deps = ["//llvm/lib/CodeGen",')
          with open(gn_file, 'w') as f:
              f.write(contents)

to update all the GN files.

(I manually removed the dep on CodeGen that this added to llvm-min-tblgen.)

Finally, I ran

    git ls-files '*.gn' '*.gni' | xargs llvm/utils/gn/gn.py format

to fix up the formatting.