compiler: add 'b_time64' base option

Introduce a new base option called `b_time64`. This is a boolean option,
which defaults to `false` (in which case it has no effect). If set to
true, this will set `_TIME_BITS=64` (or equivalent) for all
compilations.

This enables a workaround for the Y2038 problem. With `_TIME_BITS=64`,
libc will switch `time_t` and other relevant time types to 64-bits, if
not already 64-bit (i.e., this usually only affects 32-bit platforms).
libc will also transparently switch to 64-bit syscalls.

For more background information, there is an LWN article about it (from
10 years ago):

    https://lwn.net/Articles/664800/

Handling of this option is similar to _FILE_OFFSET_BITS=64, which meson
sets by default. Unfortunately, `time_t` is much more often used in
public APIs, and thus more likely to lead to ABI mismatches when mixing
code compiled with and without the option.

Author: dvdhrm

docs/markdown/Builtin-options.md

@@ -232,6 +232,7 @@ available on all platforms or with all compilers:
 | b_pgo               | off                  | off, generate, use                                            | Use profile guided optimization                                                |
 | b_sanitize          | none                 | see below                                                     | Code sanitizer to use                                                          |
 | b_staticpic         | true                 | true, false                                                   | Build static libraries as position independent                                 |
+| b_time64            | false                | true, false                                                   | Enable 64-bit time handling for 32-bit platforms (via `_TIME_BITS=64`)         |
 | b_pie               | false                | true, false                                                   | Build position-independent executables (since 0.49.0)                          |
 | b_vscrt             | from_buildtype       | none, md, mdd, mt, mtd, from_buildtype, static_from_buildtype | VS runtime library to use (since 0.48.0) (static_from_buildtype since 0.56.0)  |
 

mesonbuild/compilers/compilers.py

@@ -330,6 +330,11 @@ def get_base_compile_args(target: 'BuildTarget', compiler: 'Compiler', env: 'Env
             pass
     except KeyError:
         pass
+    try:
+        if env.coredata.get_option_for_target(target, 'b_time64'):
+            args += compiler.get_time64_args()
+    except (KeyError, AttributeError):
+        pass
     return args
 
 def get_base_link_args(target: 'BuildTarget',
@@ -1095,6 +1100,13 @@ def get_assert_args(self, disable: bool, env: 'Environment') -> T.List[str]:
         """
         return []
 
+    def get_time64_args(self) -> T.List[str]:
+        """Get arguments to enable 64-bit time handling for 32-bit platforms.
+
+        :return: A list of string arguments for this compiler
+        """
+        return []
+
     def get_crt_val(self, crt_val: str, buildtype: str) -> str:
         if crt_val in options.MSCRT_VALS:
             return crt_val

mesonbuild/compilers/mixins/clike.py

@@ -1344,6 +1344,9 @@ def get_assert_args(self, disable: bool, env: 'Environment') -> T.List[str]:
             return ['-DNDEBUG']
         return []
 
+    def get_time64_args(self) -> T.List[str]:
+        return ['-D_TIME_BITS=64']
+
     @functools.lru_cache(maxsize=None)
     def can_compile(self, src: 'mesonlib.FileOrString') -> bool:
         # Files we preprocess can be anything, e.g. .in

mesonbuild/modules/rust.py

@@ -13,7 +13,7 @@
 from .. import mesonlib, mlog
 from ..build import (BothLibraries, BuildTarget, CustomTargetIndex, Executable, ExtractedObjects, GeneratedList,
                      CustomTarget, InvalidArguments, Jar, StructuredSources, SharedLibrary, StaticLibrary)
-from ..compilers.compilers import are_asserts_disabled_for_subproject, lang_suffixes
+from ..compilers.compilers import are_asserts_disabled_for_subproject, get_option_value_for_target, lang_suffixes
 from ..interpreter.type_checking import (
     DEPENDENCIES_KW, LINK_WITH_KW, LINK_WHOLE_KW, SHARED_LIB_KWS, TEST_KWS, TEST_KWS_NO_ARGS,
     OUTPUT_KW, INCLUDE_DIRECTORIES, SOURCES_VARARGS, NoneType, in_set_validator
@@ -343,6 +343,8 @@ def bindgen(self, state: ModuleState, args: T.List, kwargs: FuncBindgen) -> Modu
                 state.environment.get_source_dir(), state.environment.get_build_dir())])
         if are_asserts_disabled_for_subproject(state.subproject, state.environment):
             clang_args.append('-DNDEBUG')
+        if get_option_value_for_target(state.environment, state.subproject, 'b_time64', False):
+            clang_args.append('-D_TIME_BITS=64')
 
         for de in kwargs['dependencies']:
             for i in de.get_include_dirs():

mesonbuild/options.py

@@ -789,6 +789,7 @@ def option_to_argparse(option: AnyOptionType, name: OptionKey, parser: argparse.
         UserComboOption(
             'b_ndebug', 'Disable asserts', 'false', choices=['true', 'false', 'if-release']),
         UserBooleanOption('b_staticpic', 'Build static libraries as position independent', True),
+        UserBooleanOption('b_time64', 'Set _TIME_BITS=64', False),
         UserBooleanOption('b_pie', 'Build executables as position independent', False),
         UserBooleanOption('b_bitcode', 'Generate and embed bitcode (only macOS/iOS/tvOS)', False),
         UserComboOption(