[GlobalISel] fix crash in IRTranslator, MachineIRBuilder when translating...

[GlobalISel] fix crash in IRTranslator, MachineIRBuilder when translating @llvm.dbg.value intrinsic and using -debug

Summary:
Fix crash when using -debug caused by the GlobalISel observer trying to print
an incomplete DBG_VALUE instruction. This was caused by the MachineIRBuilder
using buildInstr, which immediately inserts the instruction causing print,
instead of using BuildMI to first build up the instruction and using
insertInstr when finished.

Add RUN-line to existing debug-insts.ll test with -debug flag set to make sure
no crash is happening.

Also fixed a missing %s in the 2nd RUN-line of the same test.

Reviewers: t.p.northover, aditya_nandakumar, aemerson, dsanders, arsenm

Reviewed By: arsenm

Subscribers: wdng, arsenm, rovka, hiraditya, volkan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76934