ac/llvm: handle static/shared llvm init separately
Having a single init function works as expected for shared llvm, but when using a static llvm only one llvm will get initialized.
This commit separates the init function in 2:
- shared llvm = single public init function
- static llvm = one init function for each module using llvm
Fixes: 50d20dc0 ("ac/llvm: export ac_init_llvm_once in targets") Closes: #3376 (closed)