Implement riscv_vlen_asm for riscv32 #25808

Job	Run time
address_ub_sanitizer	10m 34s
basic_clang	5m 46s
basic_gcc	5m 59s
check_docs	1m 1s
check_update	1m 37s
check-ansi	2m 32s
enable_non-default_options	4m 37s
full_featured	7m 4s
fuzz_tests	3m 2s
memory_sanitizer	20m 9s
minimal	2m 32s
no-deprecated	5m 26s
non-caching	15m 57s
no-shared-macos (macos-13)	6m 9s
no-shared-ubuntu	4m 18s
no-shared-macos (macos-14)	3m 26s
self-hosted (freebsd-13.2)	12m 30s
threads_sanitizer	5m 28s
self-hosted (ubuntu-arm64-22.04)	9m 27s
external-test-cf-quiche	3m 42s
external-test-pyca (1.51.0, 3.9)	7m 27s
external-tests	10m 58s
legacy	4m 34s
no-legacy	5m 45s
out-of-readonly-source-and-install-macos (macos-13)	10m 9s
out-of-readonly-source-and-install-ubuntu	7m 28s
out-of-readonly-source-and-install-macos (macos-14)	6m 16s
	3h 3m 53s

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