Recent changes to rts.c broken with link time optimisation

[rmn30]

With the recent changes to rts.c related to setting the coverage file I get a compilation error if I try to use link time optimisation. To reproduce using one of the tests in the test directory:

sail -c ./test/c/struct.sail  > struct.c
gcc -flto -I lib/ struct.c lib/rts.c lib/sail.c lib/elf.c -lgmp -lz

which results in:

lib/rts.c:81:13: error: variable ‘sail_rts_set_coverage_file’ redeclared as function
   81 | extern void sail_rts_set_coverage_file(char *output_file);
      |             ^
struct.c:4:8: note: previously declared here
    4 | void (*sail_rts_set_coverage_file)(char *) = NULL;
      |        ^
lto1: fatal error: errors during merging of translation units
compilation terminated.
lto-wrapper: fatal error: gcc returned 1 exit status
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status

Without -flto the gcc command succeeds. I guess sail doesn't need to emit the function pointer anymore?

[rmn30]

As an aside: it's a very good idea to use link time optimisation due to many calls from generated C to small functions in rts.c.

[Alasdair]

Should be fixed by https://github.com/rems-project/sail/pull/510