[clang][ExtractAPI] Some declaration fragments are missing semicolons

[daniel-grumberg]

An example that reproduces this behavior is:

extern NSString * const MyString;

In the output, the generate declaration fragments are missing the final semicolon.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

[chaitanyav]

@daniel-grumberg i would like to give it a try, will reach out with lot of questions