[unittest][codegen] Avoid memory leak in recently added FindDebugLocT…

…est unittest

Need to finalize the DIBuilder to avoid leak sanitizer errors
like this:

Direct leak of 48 byte(s) in 1 object(s) allocated from:
    #0 0x55c99ea1761d in operator new(unsigned long)
    #1 0x55c9a518ae49 in operator new
    #2 0x55c9a518ae49 in llvm::MDTuple::getImpl(...)
    #3 0x55c9a4f1b1ec in getTemporary
    llvm#4 0x55c9a4f1b1ec in llvm::DIBuilder::createFunction(...)

llvm/unittests/CodeGen/MachineBasicBlockTest.cpp

@@ -100,6 +100,9 @@ TEST(FindDebugLocTest, DifferentIterators) {
   EXPECT_EQ(DL1, MBB.rfindPrevDebugLoc(MI2));
   EXPECT_EQ(DL1, MBB.rfindPrevDebugLoc(MI3));
   EXPECT_EQ(DL1, MBB.rfindPrevDebugLoc(MBB.instr_rbegin()));
+
+  // Finalize DIBuilder to avoid memory leaks.
+  DIB.finalize();
 }
 
 } // end namespace