compilers: pass external args to sanity check; add #include <stddef.h>

Two improvements so the compiler sanity check exercises the same code
paths as cc.links():

1. Compiler._sanity_check_compile_args (the base class) now passes
   get_external_args() and get_external_link_args() to the probe, just
   as build_wrapper_args() does.  CLikeCompiler already did this via
   _get_basic_compiler_args(); the base class fix extends it to non-CLike
   compilers (Fortran, Swift, etc.).  Duplicates in the CLike path are
   harmless because arglist deduplicates them.

2. CCompiler and CPPCompiler sanity check sources now include <stddef.h>.
   This ensures that a broken or missing include path is caught at
   compiler detection time with a natural compiler error, rather than
   surfacing later as a cryptic Meson exception.

mesonbuild/compilers/c.py

@@ -75,7 +75,7 @@ class CCompiler(CLikeCompiler, Compiler):
         return ['-nostdinc']
 
     def _sanity_check_source_code(self) -> str:
-        return 'int main(void) { int class=0; return class; }\n'
+        return '#include <stddef.h>\nint main(void) { int class=0; return class; }\n'
 
     def has_header_symbol(self, hname: str, symbol: str, prefix: str, *,
                           extra_args: T.Union[None, T.List[str], T.Callable[['CompileCheckMode'], T.List[str]]] = None,

mesonbuild/compilers/compilers.py

@@ -1366,7 +1366,9 @@ class Compiler(HoldableObject, metaclass=abc.ABCMeta):
         :return: a tuple of arguments, the first is the executable and compiler
             arguments, the second is linker arguments
         """
-        return self.exelist_no_ccache + self.get_always_args() + self.get_output_args(binname) + [sourcename], []
+        cargs = list(self.environment.coredata.get_external_args(self.for_machine, self.language))
+        largs = list(self.environment.coredata.get_external_link_args(self.for_machine, self.language))
+        return self.exelist_no_ccache + self.get_always_args() + self.get_output_args(binname) + [sourcename] + cargs, largs
 
     @abc.abstractmethod
     def _sanity_check_source_code(self) -> str:

mesonbuild/compilers/cpp.py

@@ -89,7 +89,7 @@ class CPPCompiler(CLikeCompiler, Compiler):
         return []
 
     def _sanity_check_source_code(self) -> str:
-        return 'class breakCCompiler;int main(void) { return 0; }\n'
+        return '#include <stddef.h>\nclass breakCCompiler;int main(void) { return 0; }\n'
 
     def get_compiler_check_args(self, mode: CompileCheckMode) -> T.List[str]:
         # -fpermissive allows non-conforming code to compile which is necessary