TIP: Check failed: constpool_.IsEmpty()

Describe the bug
This issue shows up when using the rebase-to-tip branch (#273).

To Reproduce
Steps to reproduce the behavior:

1. Checkout rebase-to-tip
2. Follow standard build procedure
3. Run the test:

out/riscv64.sim/cctest test-run-wasm-simd/RunWasm_I64x2ExtractWithF64x2_liftoff --random-seed=-1809348256 --nohard-abort --enable-slow-asserts --verify-heap --testing-d8-test-runner

Expected behavior
I expected this test to pass.

Errors/Logs

# Fatal error in ../../src/codegen/riscv64/assembler-riscv64.h, line 156
# Check failed: constpool_.IsEmpty().
#
#
#
#FailureMessage Object: 0x7ffcb177fb90

These tests pass while constant pools are disabled. Review this issue after #334 is resolved.