internal/rosa: create /bin symlinks via helper

This centralises the workaround for surprisingly common buggy scripts with nonstandard hardcoded paths.

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

internal/rosa/package/libcap.az

@@ -12,6 +12,7 @@ package libcap {
 	};
 
 	// uses source tree as scratch space
+	enterSource = true;
 	writable = true;
 	chmod = true;
 
@@ -20,8 +21,7 @@ package libcap {
 		"lib=lib",
 	];
 
-	early = "\nln -s ../system/bin/bash /bin/\n";
-
+	bin = [ "bash" ];
 	exec = make {
 		skipConfigure = true;
 		inPlace = true;