[mlir][llvm] Modernize the import of LLVM IR globals.

Return failure if the import of a global variable fails and add a
test case to check the emitted error message. Additionally, convert
the globals in iteration order and do not process them recursively
when translating a constant expression referencing it. Additionally,
use the module location rather unknown location.

Reviewed By: Dinistro

Differential Revision: https://reviews.llvm.org/D140966