coredata: Transform compilers in copy_as_build()

So that e.g. `c_args` is used instead of `native.c_args`.

mesonbuild/compilers/compilers.py

@@ -6,6 +6,7 @@
 
 import abc
 import contextlib, os.path, re
+import copy
 import enum
 import itertools
 import typing as T
@@ -16,7 +17,7 @@
 from .. import mesonlib
 from ..mesonlib import (
     HoldableObject,
-    EnvironmentException, MesonException,
+    EnvironmentException, MachineChoice, MesonException,
     Popen_safe_logged, LibType, TemporaryDirectoryWinProof, OptionKey,
 )
 
@@ -29,7 +30,6 @@
     from ..environment import Environment
     from ..linkers import RSPFileSyntax
     from ..linkers.linkers import DynamicLinker
-    from ..mesonlib import MachineChoice
     from ..dependencies import Dependency
 
     CompilerType = T.TypeVar('CompilerType', bound='Compiler')
@@ -463,6 +463,11 @@ def __repr__(self) -> str:
         return repr_str.format(self.__class__.__name__, self.version,
                                ' '.join(self.exelist))
 
+    def copy_for_build(self) -> Compiler:
+        new = copy.copy(self)
+        new.for_machine = MachineChoice.HOST
+        return new
+
     @lru_cache(maxsize=None)
     def can_compile(self, src: 'mesonlib.FileOrString') -> bool:
         if isinstance(src, mesonlib.File):

mesonbuild/coredata.py

@@ -626,7 +626,8 @@ def copy_as_build(self) -> CoreData:
 
         # Use only the build deps, not any host ones
         new.deps = PerMachineDefaultable(self.deps.build).default_missing()
-        new.compilers = PerMachineDefaultable(self.compilers.build).default_missing()
+        new.compilers = PerMachineDefaultable({k: v.copy_for_build() for k, v in self.compilers.build.items()}) \
+                .default_missing()
         new.cmake_cache = PerMachineDefaultable(self.cmake_cache.build).default_missing()
 
         # Drop any cross files, since this is not a cross compile