--gc:orc when is it usable (huge compile times)

[HJarausch]

Thanks to all! The `--verbosity` flag shows some `not GC-safe` warnings which I 
don't understand. Terminating the Nim compiler (in gdb) gives the following 
trace back 
    
    
    Program received signal SIGINT, Interrupt.
    0x0000555555be8afc in hash_injectdestructors_188 ()
    (gdb) where
    #0  0x0000555555be8afc in hash_injectdestructors_188 ()
    #1  0x0000555555bed4e7 in aliasesCached_injectdestructors_121 ()
    #2  0x0000555555bf56d0 in 
computeLastReadsAndFirstWrites_injectdestructors_3786
        ()
    #3  0x0000555555c20434 in injectDestructorCalls_injectdestructors_10218 ()
    #4  0x0000555555d46240 in genTopLevelStmt_cgen_29426 ()
    #5  0x0000555555d4638e in myProcess_cgen_29434 ()
    #6  0x00005555558c3d38 in processTopLevelStmt_passes_138 ()
    #7  0x00005555558c4a5c in processModule_passes_231 ()
    #8  0x0000555555d6723e in compileModule_modules_1709 ()
    #9  0x0000555555d6b622 in compileProject_modules_2894 ()
    #10 0x0000555555ec1e9e in commandCompileToC_main_363 ()
    #11 0x0000555555ec2562 in compileToBackend_main_534 ()
    #12 0x0000555555ec5099 in mainCommand_main_504 ()
    #13 0x0000555555ecbbce in handleCmdLine_nim_41 ()
    #14 0x0000555555ecc67e in NimMainModule ()
    #15 0x0000555555ecc582 in NimMain ()
    #16 0x000055555557096d in main ()
    
    
    Run

I have put 3 files into Pastebin which should compile with just the standard 
libraries installed. `pastebin.com/LwvSpGyx` `pastebin.com/AmU4CDcW` 
`pastebin.com/BH9mBAs2`

These file expire on Sunday October 3rd

Thanks for looking into this problem, Helmut