Make program_invocation_name modifiable

libiconv expects program_invocation_name to be an lvalue
5 jobs for mut-program_invocation_name in 13 minutes and 56 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #20408
build:linux

00:07:30

passed #20409
build:redox

00:07:26

 
  Test
failed #20412
allowed to fail
fmt

00:01:09

passed #20410
test:linux

00:00:48

passed #20411
test:redox

00:06:25

 
Name Stage Failure
failed
fmt Test
+            Some(DestBuffer {
+ ptr: buf as *mut u8,
+ len: size,
+ }),
+ ),
out,
result,
)
ERROR: Job failed: exit code 1