Hand crafted Fib bundle compiling failure

Description

When compiling a hand crafted FIbonacci performance measurement Mu bundle, Zebu fails with the following message yet Holstein succeeds:

TRACE - instsel on node#1103 (STORE  NotAtomic (%m.c.v.b.irheadnxt #1090 = GETFIELDIREF  (%m.c.v.b.irhead #1089 = GETIREF %m.c.v.b.head #1088) 2) NullRef)
TRACE - instsel on STORE
thread '<unnamed>' panicked at 'a struct type does not have a layout yet: BackendTypeInfo { size: 8, alignment: 8, struct_layout: None, elem_padded_size: None, gc_type: GCType { id: 2, alignment: 8, fix_size: 8, fix_refs: Some(Map { offsets: [0], size: 8 }), var_refs: None, var_size: None } }', src/compiler/backend/arch/x86_64/inst_sel.rs:4640

Bug Reproduction

• Clone mu/mu-perf-benchmarks repository and checkout mu-perf-benchmarks@b1893146 (zebu_bug) branch.
• Edit example/zebu_bug.yml and set the correct MU_ZEBU environment variable.
• run example/zebu_bug.yml with python3 mubench local example/zebu_bug.yml, and check the error log file example/fib_mu_zebu.log.