internal/rosa/toybox: do not assume bash location

For compatibility with Gentoo stage3 as bootstrap seed.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/toybox.go

@@ -17,7 +17,7 @@ func (t Toolchain) newToybox(suffix, script string) pkg.Artifact {
 		"ROSA_CHECK=make USER=cure tests",
 	), `
 chmod +w /bin/
-ln -sf ../system/bin/bash /bin/
+ln -rs "$(which bash)" /bin/ || true
 
 cd /usr/src/toybox
 chmod +w kconfig tests