envkernel.sh: fallback to old armhf hostspec (!1786)

The armhf hostspec triplet has changed during the Alpine 3.6 release
cylcle. It was recently adjusted in abuild's arch_to_hostspec()
function [1]. Cross compilers in postmarketOS that were built with a
previous version of abuild still have the old hostspec in the name.
Since we use the same function in envkernel.sh to get the cross compiler
name, it is currently failing here for armhf.

We can't simply bump the pkgrel to force a rebuild, because that would
make them go out of sync with the upstrem (non-cross) compiler packages.
That would break the workflow for fixing incompatibilities with Alpine
(see [2]).

Add a workaround to envkernel.sh, to detect if the installed armhf cross
compiler binaries still have the old name.

[1] https://github.com/alpinelinux/abuild/pull/56
[2] https://wiki.postmarketos.org/wiki/Repository_maintenance

helpers/envkernel.sh

@@ -178,6 +178,19 @@ set_alias_make() {
 		cross_compiler="/usr/bin/$prefix-"
 	fi
 
+	# Workaround for issue #1784 (can be removed after the following packages
+	# have been rebuilt with current abuild: binutils-armhf, gcc-armhf,
+	# gcc4-armhf, gcc6-armhf, musl-armhf)
+	if [ "$deviceinfo_arch" = "armhf" ] \
+			&& ! [ -e "${chroot}${cross_compiler}gcc" ]; then
+		echo "NOTE: using old armhf cross compiler name (#1784)"
+		_old="armv6-alpine-linux-muslgnueabihf"
+		_new="armv6-alpine-linux-musleabihf"
+		cc="$(echo "$cc" | sed "s/$_new/$_old/")"
+		cross_compiler="$(echo "$cross_compiler" | sed "s/$_new/$_old/")"
+		unset _old _new
+	fi
+
 	# Build make command
 	cmd="echo '*** pmbootstrap envkernel.sh active for $PWD! ***';"
 	cmd="$cmd pmbootstrap -q chroot --user --"