Fix a bug that would cause subzero to fail when --threads=0.

tests_lit/llvm2ice_tests/elf_container.ll

 ; Tests that we generate an ELF container with fields that make sense,
 ; cross-validating against llvm-mc.
 
 ; For the integrated ELF writer, we can't pipe the output because we need
 ; to seek backward and patch up the file headers. So, use a temporary file.
 ; RUN: %p2i -i %s --filetype=obj --args -O2 --verbose none -o %t \
 ; RUN:   && llvm-readobj -file-headers -sections -section-data \
 ; RUN:       -relocations -symbols %t | FileCheck %s
 
 ; RUN: %if --need=allow_dump --command %p2i -i %s --args -O2 --verbose none \
@@ skipping 252 matching lines @@
 ; CHECK:   }
 ; CHECK:   Section {
 ; CHECK:     Index: {{[1-9][0-9]*}}
 ; CHECK:     Name: .rodata
 ; CHECK:     Type: SHT_PROGBITS
 ; CHECK:     Flags [ (0x2)
 ; CHECK:       SHF_ALLOC
 ; CHECK:     ]
 ; CHECK:     Address: 0x0
 ; CHECK:     Offset: 0x{{[1-9A-F][0-9A-F]*}}
-; Size is 56 instead of 48 due to __Sz_block_profile_info .
-; CHECK:     Size: 56
+; CHECK:     Size: 48
 ; CHECK:     Link: 0
 ; CHECK:     Info: 0
 ; CHECK:     AddressAlignment: 32
 ; CHECK:     EntrySize: 0
 ; CHECK:     SectionData (
 ; CHECK:       0000: 616203FF F66667{{.*}} |ab...fg
 ; CHECK:     )
 ; CHECK:   }
 ; CHECK:   Section {
 ; CHECK:     Index: {{[1-9][0-9]*}}
@@ skipping 354 matching lines @@
 ; CHECK:        Symbol {
 ; CHECK:          Name: memset
 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Global
 ; CHECK-NEXT:     Type: None
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: Undefined
 ; CHECK-NEXT:   }
 ; CHECK: ]