[GlobalISel] Remove debug locations when emitting constants.

The tl;dr story is that this causes jumps in the emitted line
tables, even at `-O0`. We could at some point consider more fancy
solutions to preserve locations, but it doesn't seem to be worth
the effort for now.

<rdar://problem/62460788>

Differential Revision:  https://reviews.llvm.org/D78947

llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

@@ -290,6 +290,7 @@ MachineInstrBuilder MachineIRBuilder::buildConstant(const DstOp &Res,
   }
 
   auto Const = buildInstr(TargetOpcode::G_CONSTANT);
+  Const->setDebugLoc(DebugLoc());
   Res.addDefToMIB(*getMRI(), Const);
   Const.addCImm(&Val);
   return Const;

llvm/test/CodeGen/AArch64/GlobalISel/constant-dbg-loc.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-; RUN: llc -mtriple aarch64 -O0 -stop-after=irtranslator -global-isel -verify-machineinstrs %s -o - 2>&1 | FileCheck %s
+; RUN: llc -mtriple aarch64 -O0 -stop-after=irtranslator -global-isel -verify-machineinstrs %s -o - 2>&1 | FileCheck --match-full-lines %s
 target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
 target triple = "arm64-apple-ios5.0.0"
 
@@ -13,8 +13,8 @@ define i32 @main() #0 !dbg !14 {
   ; CHECK:   successors: %bb.2(0x40000000), %bb.3(0x40000000)
   ; CHECK:   [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
   ; CHECK:   [[GV:%[0-9]+]]:_(p0) = G_GLOBAL_VALUE @var1, debug-location !DILocation(line: 0, scope: !18)
-  ; CHECK:   [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1, debug-location !DILocation(line: 0, scope: !18)
-  ; CHECK:   [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2, debug-location !DILocation(line: 0, scope: !22)
+  ; CHECK:   [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+  ; CHECK:   [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
   ; CHECK:   [[GV1:%[0-9]+]]:_(p0) = G_GLOBAL_VALUE @var2, debug-location !DILocation(line: 0, scope: !22)
   ; CHECK:   [[FRAME_INDEX:%[0-9]+]]:_(p0) = G_FRAME_INDEX %stack.0.retval
   ; CHECK:   G_STORE [[C]](s32), [[FRAME_INDEX]](p0) :: (store 4 into %ir.retval)