Tag the 10.0.0 version bump.

The tag name, llvmorg-10-init, signifies that this is the initial commit
with major version number 10.

With this tag in place, git-describe can be used to generate nicer
names for commits on master, for example:

  $ git describe <hash>
  llvmorg-10-init-<number>-g<hash>

where <number> is the number of commits since this tag.

The plan is to add this kind of tag together with future version bumps.

Creating release candidate final from release_900 branch

llvm-svn: 372316

Creating release candidate rc6 from release_900 branch

llvm-svn: 372115

Creating release candidate rc5 from release_900 branch

llvm-svn: 371837

Creating release candidate rc4 from release_900 branch

llvm-svn: 371500

Creating release candidate rc3 from release_900 branch

llvm-svn: 370469

Creating release candidate rc2 from release_900 branch

llvm-svn: 368708

Creating release candidate rc1 from release_900 branch

llvm-svn: 367223

Creating release candidate final from release_801 branch

llvm-svn: 366581

Creating release candidate rc4 from release_801 branch

llvm-svn: 365728