Add AllTargetsBindings sublibrary instead of having static inlines in the llvm-c...

Add AllTargetsBindings sublibrary instead of having static inlines in the llvm-c headers.

This new library will be linked in when using the "all-targets"
component and contains the LLVMInitializeAll* functions.

This means that those functions will exist as real symbols in
the shared library, and can therefore can be called from
bindings that are using ffi the shared library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192690 91177308-0d34-0410-b5e6-96231b3b80d8