kernel-build.eclass: add HPPA support

Support HPPA kernel builds.

Notes:
- HPPA 2.0 supports 32-bit and 64-bit kernels (HPPA 2.0 userland remains
  32-bit for now as toolchain support isn't there yet for 64-bit).

  I've decided to only accommodate 64-bit kernels here unless/until someone
  requests & can help figure out an acceptable solution for 32-bit kernels
  for HPPA 2.0.

- HPPA 1.x should be fine as there's no need for a cross-compiler there,
  unlike HPPA 2.x for 64-bit (sys-devel/kgcc64). It should Just Work,
  but not tested.

Not adding a BDEPEND on sys-devel/kgcc64 as it's unclear how to do this
cleanly only for HPPA 2.0.

Tested on RP3440 and C8000.

Signed-off-by: Sam James <sam@gentoo.org>

eclass/kernel-build.eclass

@@ -1,4 +1,4 @@
-# Copyright 2020-2021 Gentoo Authors
+# Copyright 2020-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 # @ECLASS: kernel-build.eclass
@@ -52,6 +52,20 @@ BDEPEND="
 kernel-build_src_configure() {
 	debug-print-function ${FUNCNAME} "${@}"
 
+	if ! tc-is-cross-compiler && use hppa ; then
+		if [[ ${CHOST} == hppa2.0-* ]] ; then
+			# Only hppa2.0 can handle 64-bit anyway.
+			# Right now, hppa2.0 can run both 32-bit and 64-bit kernels,
+			# but it seems like most people do 64-bit kernels now
+			# (obviously needed for more RAM too).
+
+			# TODO: What if they want a 32-bit kernel?
+			# Not too worried about this case right now.
+			elog "Forcing 64 bit (${CHOST/2.0/64}) build..."
+			export CHOST=${CHOST/2.0/64}
+		fi
+	fi
+
 	# force ld.bfd if we can find it easily
 	local LD="$(tc-getLD)"
 	if type -P "${LD}.bfd" &>/dev/null; then