eclass/toolchain: Sync with Gentoo

It's from Gentoo commit a7c27596827072f586dc07e6d53531ecb2c7cd6e.

sdk_container/src/third_party/portage-stable/eclass/toolchain.eclass

@@ -288,6 +288,13 @@ BDEPEND="
 	)"
 DEPEND="${RDEPEND}"
 
+if [[ ${PN} == gcc && ${PV} == *_p* ]] ; then
+	# Snapshots don't contain info pages.
+	# If they start to, adjust gcc_cv_prog_makeinfo_modern logic in toolchain_src_configure.
+	# Needed unless/until https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106899 is fixed
+	BDEPEND+=" sys-apps/texinfo"
+fi
+
 if tc_has_feature gcj ; then
 	DEPEND+="
 		gcj? (
@@ -324,11 +331,19 @@ if tc_has_feature zstd ; then
 	RDEPEND+=" zstd? ( app-arch/zstd:= )"
 fi
 
-if tc_has_feature valgrind; then
+if tc_has_feature valgrind ; then
 	BDEPEND+=" valgrind? ( dev-util/valgrind )"
 fi
 
-if tc_version_is_at_least 12.0 ; then
+# TODO: Add a pkg_setup & pkg_pretend check for whether the active compiler
+# supports Ada.
+if tc_has_feature ada ; then
+	BDEPEND+=" ada? ( || ( sys-devel/gcc[ada] dev-lang/gnat-gpl[ada] ) )"
+fi
+
+# TODO: Add a pkg_setup & pkg_pretend check for whether the active compiler
+# supports D.
+if tc_has_feature d && tc_version_is_at_least 12.0 ; then
 	# D in 12+ is self-hosting and needs D to bootstrap.
 	# TODO: package some binary we can use, like for Ada
 	# bug #840182
@@ -1187,8 +1202,6 @@ toolchain_src_configure() {
 				fi
 			done
 
-			# Convert armv6m to armv6-m
-			[[ ${arm_arch} == armv6m ]] && arm_arch=armv6-m
 			# Convert armv7{a,r,m} to armv7-{a,r,m}
 			[[ ${arm_arch} == armv7? ]] && arm_arch=${arm_arch/7/7-}
 			# See if this is a valid --with-arch flag
@@ -1213,6 +1226,17 @@ toolchain_src_configure() {
 					armv7*) confgcc+=( --with-fpu=vfpv3-d16 ) ;;
 				esac
 			fi
+
+			# If multilib is used, make the compiler build multilibs
+			# for A or R and M architecture profiles. Do this only
+			# when no specific arch/mode/float is specified, e.g.
+			# for target arm-none-eabi, since doing this is
+			# incompatible with --with-arch/cpu/float/fpu.
+			if is_multilib && [[ ${arm_arch} == arm ]] && \
+			   tc_version_is_at_least 7.1
+			then
+				confgcc+=( --with-multilib-list=aprofile,rmprofile  )
+			fi
 			;;
 		mips)
 			# Add --with-abi flags to set default ABI
@@ -1408,9 +1432,22 @@ toolchain_src_configure() {
 		)
 	fi
 
-	# Disable gcc info regeneration -- it ships with generated info pages
+	if [[ ${PV} != *_p* && -f "${S}"/gcc/doc/gcc.info ]] ; then
-	# already.  Our custom version/urls/etc... trigger it. bug #464008
+		# Disable gcc info regeneration -- it ships with generated info pages
-	export gcc_cv_prog_makeinfo_modern=no
+		# already.  Our custom version/urls/etc... trigger it. bug #464008
+		export gcc_cv_prog_makeinfo_modern=no
+	else
+		# Allow a fallback so we don't accidentally install no docs
+		# bug #834845
+		ewarn "No pre-generated info pages in tarball. Allowing regeneration with texinfo..."
+
+		if [[ ${PV} == *_p* && -f "${S}"/gcc/doc/gcc.info ]] ; then
+			# Safeguard against https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106899 being fixed
+			# without corresponding ebuild changes.
+			eqawarn "Snapshot release with pre-generated info pages found!"
+			eqawarn "The BDEPEND in the ebuild should be updated to drop texinfo."
+		fi
+	fi
 
 	# Do not let the X detection get in our way.  We know things can be found
 	# via system paths, so no need to hardcode things that'll break multilib.