Genode fixes (#8501)

* Genode fixes

- wrap strings in "Genode::Cstring" when logging
- define SIGABRT for Genode
- disable GCC -fstack-protector
- use log RPC for fatal messages
- add --os:genode build to appveyor
- define paramStr and paramCount

* Select fixups for Genode POSIX

lib/system/ansi_c.nim

@@ -50,7 +50,7 @@ when defined(windows):
     SIGTERM = cint(15)
 elif defined(macosx) or defined(linux) or defined(freebsd) or
      defined(openbsd) or defined(netbsd) or defined(solaris) or
-     defined(dragonfly) or defined(nintendoswitch):
+     defined(dragonfly) or defined(nintendoswitch) or defined(genode):
   const
     SIGABRT = cint(6)
     SIGFPE = cint(8)

lib/system/excpt.nim

@@ -31,7 +31,11 @@ proc showErrorMessage(data: cstring) {.gcsafe.} =
   if errorMessageWriter != nil:
     errorMessageWriter($data)
   else:
-    writeToStdErr(data)
+    when defined(genode):
+      # stderr not available by default, use the LOG session
+      echo data
+    else:
+      writeToStdErr(data)
 
 proc quitOrDebug() {.inline.} =
   when not defined(endb):