Add support for the CompCert C Compiler

* Add preliminary support for the CompCert C Compiler

The intention is to use this with the picolibc, so some GCC flags are
automatically filtered. Since CompCert uses GCC is for linking, those
GCC-linker flags which are used by picolibc, are automatically prefixed
with '-WUl', so that they're passed to GCC.

Squashed commit of the following:

commit 4e0ad66dca9de301d2e41e74aea4142afbd1da7d
Author: Sebastian Meyer <meyer@absint.com>
Date:   Mon Aug 31 14:20:39 2020 +0200

    remove '-fall' from default arguments, also filter -ftls-model=.*

commit 41afa3ccc62ae72824eb319cb8b34b7e6693cb67
Author: Sebastian Meyer <meyer@absint.com>
Date:   Mon Aug 31 14:13:55 2020 +0200

    use regex for filtering ccomp args

commit d68d242d0ad22f8bf53923ce849da9b86b696a75
Author: Sebastian Meyer <meyer@absint.com>
Date:   Mon Aug 31 13:54:36 2020 +0200

    filter some gcc arguments

commit 982a01756266bddbbd211c54e8dbfa2f43dec38f
Author: Sebastian Meyer <meyer@absint.com>
Date:   Fri Aug 28 15:03:14 2020 +0200

    fix ccomp meson configuration

commit dce0bea00b1caa094b1ed0c6c77cf6c12f0f58d9
Author: Sebastian Meyer <meyer@absint.com>
Date:   Thu Aug 27 13:02:19 2020 +0200

    add CompCert to meson (does not fully work, yet)

* remove unused import and s/cls/self/

fixes the two obvious LGTM warnings

* CompCert: Do not ignore unsupported GCC flags

Some are safe to ignore, however, as per
https://github.com/mesonbuild/meson/pull/7674, they should not be
ignored by meson itself. Instead the meson.build should take care to
select only those which are actually supported by the compiler.

* remove unused variable

* Only add arguments once.

* Apply suggestions from code review

Co-authored-by: Dylan Baker <dylan@pnwbakers.com>

* Remove erroneous ' ' from '-o {}'.format()

As noticed by @dcbaker

* added release note snippet for compcert

* properly split parameters

As suggested by @dcbaker, these parameters should be properly split into multiple strings.

Co-authored-by: Dylan Baker <dylan@pnwbakers.com>

* Update add_compcert_compiler.md

Added a sentence about the state of the implementation (experimental); use proper markdown

* properly separate arguments

Co-authored-by: Dylan Baker <dylan@pnwbakers.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/mesonbuild/linkers.py b/mesonbuild/linkers.py
index 3f65da1..b6e6443 100644
--- a/mesonbuild/linkers.py
+++ b/mesonbuild/linkers.py
@@ -230,6 +230,18 @@ class Xc16Linker(StaticLinker):
     def get_linker_always_args(self) -> T.List[str]:
         return ['rcs']
 
+class CompCertLinker(StaticLinker):
+
+    def __init__(self, exelist: T.List[str]):
+        super().__init__(exelist)
+        self.id = 'ccomp'
+
+    def can_linker_accept_rsp(self) -> bool:
+        return False
+
+    def get_output_args(self, target: str) -> T.List[str]:
+        return ['-o{}'.format(target)]
+
 
 class C2000Linker(StaticLinker):
 
@@ -869,6 +881,47 @@ class Xc16DynamicLinker(DynamicLinker):
                          install_rpath: str) -> T.Tuple[T.List[str], T.Set[bytes]]:
         return ([], set())
 
+class CompCertDynamicLinker(DynamicLinker):
+
+    """Linker for CompCert C compiler."""
+
+    def __init__(self, for_machine: mesonlib.MachineChoice,
+                 *, version: str = 'unknown version'):
+        super().__init__('ccomp', ['ccomp'], for_machine, '', [],
+                         version=version)
+
+    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')
+
+    def get_accepts_rsp(self) -> bool:
+        return False
+
+    def get_lib_prefix(self) -> str:
+        return '-l'
+
+    def get_std_shared_lib_args(self) -> T.List[str]:
+        return []
+
+    def get_output_args(self, outputname: str) -> T.List[str]:
+        return ['-o{}'.format(outputname)]
+
+    def get_search_args(self, dirname: str) -> T.List[str]:
+        return ['-L{}'.format(outputname)]
+
+    def get_allow_undefined_args(self) -> T.List[str]:
+        return []
+
+    def get_soname_args(self, env: 'Environment', prefix: str, shlib_name: str,
+                        suffix: str, soversion: str, darwin_versions: T.Tuple[str, str],
+                        is_shared_module: bool) -> T.List[str]:
+        raise mesonlib.MesonException('{} does not support shared libraries.'.format(self.id))
+
+    def build_rpath_args(self, env: 'Environment', build_dir: str, from_dir: str,
+                         rpath_paths: str, build_rpath: str,
+                         install_rpath: str) -> T.Tuple[T.List[str], T.Set[bytes]]:
+        return ([], set())
 
 class C2000DynamicLinker(DynamicLinker):