Fix codegen of Memory-repr enum payload accesses #1778

Job	Run time
cargo-deny	1m 7s
release-dry-run	3m 33s
Android (ubuntu-latest, aarch64-linux-android)	3m 32s
Compiletest (ubuntu-latest)	3m 32s
Test (windows-latest)	3m 31s
Compiletest (windows-latest)	3m 30s
Difftest (windows-latest)	3m 31s
Difftest (macOS-latest)	3m 35s
cargo-gpu-os (ubuntu-latest)	3m 32s
Lint	3m 25s
Difftest (ubuntu-latest)	3m 32s
cargo-gpu-os (windows-latest)	3m 32s
Test (ubuntu-latest)	3m 32s
Test (macOS-latest)	3m 34s
Compiletest (macOS-latest)	3m 35s
cargo-gpu-os (macos-latest)	3m 36s
cargo-gpu-backwards-compat (eea8998df9dc2fd8e7a65c5b5b7ae20c238a665a, 0.29.3)	2m 9s
cargo-gpu-backwards-compat (877bd8697a15f3e6d09446a5e1807e6237ca1dac)	2m 21s
cargo-gpu-backwards-compat (30896871ba00e668029ccb724f1438202b284708)	2m 21s
cargo-gpu-backwards-compat (0.9.0, 0.24.2)	2m 21s
cargo-gpu-backwards-compat (2326b87fe1542eeb898065e36ac949307b55386d, =0.30.7)	2m 21s
cargo-gpu-backwards-compat (a27c0363d391a54de1feb9ee6864ad9dff72d243, 0.33.0)	2m 17s
cargo-gpu-backwards-compat (e767f24f2565baf1a71bbaf84d453d181cab2417)	2m 9s
cargo-gpu-backwards-compat (f79c4181a5dc2d37303947b113f190930c6c1ce6, =0.30.7)	2m 9s
test_success	2s
	1h 12m 19s

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