[Bug libstdc++/91947] std::filesystem::file_size will return wrong value on 32bit platforms with large files support

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91947

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think this is simpler and less likely to cause problems:

# This header is not installed, it's only used to build libstdc++ itself.
${host_builddir}/largefile-config.h: ${CONFIG_HEADER}
        @rm -f $@.tmp
        @-grep 'define _DARWIN_USE_64_BIT_INODE' ${CONFIG_HEADER} >> $@.tmp
        @-grep 'define _FILE_OFFSET_BITS' ${CONFIG_HEADER} >> $@.tmp
        @-grep 'define _LARGE_FILES' ${CONFIG_HEADER} >> $@.tmp
        @mv $@.tmp $@