Issues installing rustup with OpenIndiana / Illumos

When trying to install rustup on new install of OpenIndiana Hipster 21.04 in a virtualbox VM, I browsed over to https://rustup.rs and got the following message:

I don't recognize your platform.

rustup runs on Windows, Linux, macOS, FreeBSD, NetBSD, and illumos. If you are on one of these platforms and are seeing this then please report an issue, along with the following values:
navigator.platform:
SunOS i86pc
navigator.appVersion:
5.0 (X11)

...but there was then a note with instructions to run:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

...that didn't make it very far. Apparently the default bourne shell doesn't like that. Bash seemed to fare better, but dies when executing the rust-init executable that it downloads from:

https://static.rust-lang.org/rustup/dist/x86_64-unknown-illumos/rustup-init

...with an error message:

ld.so.1: rustup-init: fatal: libgcc_s.so.1: open failed: No such file or directory

...but there are many versions of libgcc_s.so.1 installed:

$ find . -name "libgcc_s.so.1" 2>/dev/null
./usr/sfw/lib/amd64/libgcc_s.so.1
./usr/sfw/lib/libgcc_s.so.1
./usr/gcc/7/lib/amd64/libgcc_s.so.1
./usr/gcc/7/lib/libgcc_s.so.1
./usr/gcc/3.4/lib/libgcc_s.so.1
./usr/gcc/3.4/lib/amd64/libgcc_s.so.1
./usr/gcc/10/lib/amd64/libgcc_s.so.1
./usr/gcc/10/lib/libgcc_s.so.1

for reference on this machine:

$ uname -a
SunOS oi 5.11 illumos-fa4a3e77ed i86pc i386 i86pc

Start with the rustup.rs detection flow and the shell command shown in the report, then investigate the rustup-init download for x86_64-unknown-illumos. Reproduce the failure on OpenIndiana or illumos, including the missing libgcc_s.so.1 error. Done means the supported-platform installation path works on the reported system or the compatibility limitation is clearly handled.