Worked for me on two machines:
/usr/pkg/bin/rustc: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 9.99.95, not stripped
/usr/pkg/bin/rustc: ELF 64-bit MSB pie executable, SPARC V9, total store ordering, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 9.99.95, not stripped
rustc 1.58.1
arm64# file /usr/pkg/bin/rustc
/usr/pkg/bin/rustc: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 9.99.94, not stripped
armv7# file /usr/pkg/bin/rustc
/usr/pkg/bin/rustc: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 9.99.93, compiled for: earmv7hf, not stripped
earmv6hf: can't build