Some fixes for CompCert

1. Like with gcc's `ld`, also use the `group_start` code to create a
   `--start-group`/`--end-group`
2. xc16 tricked into believing the 'link_whole' was about `--*-group`,
   but it should use gcc's `--whole-archive` instead.
3. Not clear what the get_lib_prefix should really do, but for picolibc
   it seems I want just `''`.

The problem with picolibc was that the `-l` would be prefixed to a lib
like `picolib/libm/libm.a`. Though of course the `-l` would be necessary
for just a plain `m` (that's what I assumed this would be used for).
I think this might need some clarification from the meson devs ;-)

1 files changed, 2 insertions, 2 deletions

diff --git a/mesonbuild/linkers.py b/mesonbuild/linkers.py
index 02b30e9..d85c88e 100644
--- a/mesonbuild/linkers.py
+++ b/mesonbuild/linkers.py
@@ -900,13 +900,13 @@ class CompCertDynamicLinker(DynamicLinker):
     def get_link_whole_for(self, args: T.List[str]) -> T.List[str]:
         if not args:
             return args
-        return self._apply_prefix('-WUl,--start-group') + args + self._apply_prefix('-WUl,--end-group')
+        return self._apply_prefix('-Wl,--whole-archive') + args + self._apply_prefix('-Wl,--no-whole-archive')
 
     def get_accepts_rsp(self) -> bool:
         return False
 
     def get_lib_prefix(self) -> str:
-        return '-l'
+        return ''
 
     def get_std_shared_lib_args(self) -> T.List[str]:
         return []