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/ninja.az

@@ -15,6 +15,7 @@ package ninja {
 		"CFLAGS=-std=c++17",
 	];
 
+	bin = [ "echo" ];
 	exec = generic {
 		build = `
 python3 /usr/src/ninja/configure.py \
@@ -22,12 +23,10 @@ python3 /usr/src/ninja/configure.py \
 	--bootstrap
 python3 /usr/src/ninja/configure.py \
 	--gtest-source-dir=/usr/src/extra/googletest
-./ninja ` + jobsFlagE + ` all`;
+./ninja ` + jobsFlagE + ` all
+`;
 
-		check = `
-chmod +w /bin/
-ln -s ../system/bin/echo /bin/
-./ninja_test`;
+		check = "./ninja_test";
 
 		install = `
 mkdir -p /work/system/bin/