Only allocate the minimal alignment requested for a type when possible. #4249

Job	Run time
rustfmt	13s
test_llvm	4m 7s
bench	7m 23s
test (ubuntu-latest, riscv64gc-unknown-linux-gnu, gcc-riscv64-linux-gnu qemu-user)	4m 40s
test (macos-15-intel, x86_64-apple-darwin)	25m 17s
test (ubuntu-24.04-arm, aarch64-unknown-linux-gnu)	9m 51s
test (macos-latest, aarch64-apple-darwin)	10m 53s
test (ubuntu-latest, s390x-unknown-linux-gnu, gcc-s390x-linux-gnu qemu-user)	4m 44s
dist (ubuntu-22.04, x86_64-unknown-linux-gnu)	1m 54s
dist (ubuntu-24.04-arm, aarch64-unknown-linux-gnu)	1m 43s
test (windows-latest, x86_64-pc-windows-msvc)	18m 46s
test (windows-latest, x86_64-pc-windows-gnu)	23m 37s
test (ubuntu-latest, x86_64-unknown-linux-gnu)	12m 4s
dist (windows-latest, x86_64-pc-windows-gnu)	3m 8s
dist (macos-15-intel, x86_64-apple-darwin)	2m 52s
dist (windows-latest, x86_64-pc-windows-msvc)	2m 22s
dist (macos-latest, aarch64-apple-darwin)	1m 52s
release	0s
	2h 15m 26s

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