libstdc++: Install <coroutine> header for freestanding [PR103726]

The standard says that <coroutine> should be present for freestanding.
That was intentionally left out of the initial implementation, but can
be done without much trouble. The header should be moved to libsupc++ at
some point in stage 1.

The standard also says that <coroutine> defines a std::hash
specialization, which was missing from our implementation. That's a
problem for freestanding (see LWG 3653) so only do that for hosted.

We can use concepts to constrain the __coroutine_traits_impl base class
when compiled with concepts enabled. In a pure C++20 implementation we
would not need that base class at all and could just use a constrained
partial specialization of coroutine_traits. But the absence of the
__coroutine_traits_impl<R, void> base would create an ABI difference
between the non-standard C++14/C++17 support for coroutines and the same
code compiled as C++20. If we drop support for <coroutine> pre-C++20 we
should revisit this.

libstdc++-v3/ChangeLog:

	PR libstdc++/103726
	* include/Makefile.am: Install <coroutine> for freestanding.
	* include/Makefile.in: Regenerate.
	* include/std/coroutine: Adjust headers and preprocessor
	conditions.
	(__coroutine_traits_impl): Use concepts when available.
	[_GLIBCXX_HOSTED] (hash<coroutine_handle>): Define.

1 files changed, 2 insertions, 2 deletions

diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index 0031f54f3fa..4ab942ae666 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/libstdc++-v3/include/Makefile.in
@@ -1906,7 +1906,7 @@ ${pch3_output}: ${pch3_source} ${pch2_output}
 # This is a subset of the full install-headers rule.  We only need <ciso646>,
 # <cstddef>, <cfloat>, <limits>, <climits>, <version>, <cstdint>, <cstdlib>,
 # <new>, <typeinfo>, <exception>, <initializer_list>, <cstdalign>, <cstdarg>,
-# <concepts>, <cstdbool>, <type_traits>, <bit>, <atomic>,
+# <concepts>, <coroutine>, <cstdbool>, <type_traits>, <bit>, <atomic>,
 # and any files which they include (and which we provide).
 # <new>, <typeinfo>, <exception>, <initializer_list> and <compare>
 # are installed by libsupc++, so only the others and the sub-includes
@@ -1921,7 +1921,7 @@ install-freestanding-headers:
 	  ${glibcxx_srcdir}/$(CPU_DEFINES_SRCDIR)/cpu_defines.h; do \
 	  $(INSTALL_DATA) $${file} $(DESTDIR)${host_installdir}; done
 	$(mkinstalldirs) $(DESTDIR)${gxx_include_dir}/${std_builddir}
-	for file in limits type_traits atomic bit concepts version; do \
+	for file in limits type_traits atomic bit concepts coroutine version; do \
 	  $(INSTALL_DATA) ${std_builddir}/$${file} $(DESTDIR)${gxx_include_dir}/${std_builddir}; done
 	$(mkinstalldirs) $(DESTDIR)${gxx_include_dir}/${c_base_builddir}
 	for file in ciso646 cstddef cfloat climits cstdint cstdlib \