libstdc++: Add <bits/binders.h> to freestanding headers [PR125112]
Fixes freestanding builds of libstdc++ by including <bits/binders.h>.
This commit fixes a build issue in libstdc++ when using the --disable-libstdcxx-hosted option, which configures the library for freestanding environments. The <ranges> header, recently added to the freestanding headers, depends on <bits/binders.h>. This commit moves <bits/binders.h> to the freestanding headers, resolving the dependency and allowing <ranges> to be used in freestanding builds.
In Details
The libstdc++ build system distinguishes between "hosted" and "freestanding" environments. Freestanding environments, indicated by --disable-libstdcxx-hosted, target systems without an operating system, like embedded systems. The <ranges> header, introduced in r16-3575-g1a41e52d7ecb58, depends on <bits/binders.h>. This commit updates include/Makefile.am to move <bits/binders.h> from bits_headers to bits_freestanding, correcting the build configuration and enabling <ranges> in freestanding mode. This resolves PR125112.
For Context
The C++ standard library (libstdc++ in GCC) provides a wide range of functions and data structures. Some parts of the library are designed to work in any environment, including those without an operating system (so-called "freestanding" environments, often used in embedded systems development). This commit fixes an issue where a header file (<bits/binders.h>) required by a newer feature (<ranges>) was not correctly included in the set of headers available in freestanding environments. This change ensures that the <ranges> feature can be used in these environments, expanding the capabilities of C++ for bare-metal and embedded development.