ERROR: Cannot find cbindgen on RPI2 running 12-stable

[bob prohaska]

In trying to compile firefox on an RPI2 running 12-stable the system reports
ERROR: Cannot find cbindgen. Please run `mach bootstrap`,
`cargo install cbindgen`, ensure that `cbindgen` is on your PATH,
or point at an executable with `CBINDGEN`.

Attempts to follow the instructions produce a chain of errors, starting
with "permission denied" at running mach. Making mach executable causes
a furthter chain of file not found errors.

Uname -a reports
12.1-STABLE r355279 RPI2

Ports are at 518859

Thanks for reading,

bob prohaska