internal/rosa/cmake: chmod entire source tree

This works around builds that traverse out of the appended pathname.

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

internal/rosa/cmake.go

@@ -92,7 +92,7 @@ func (t Toolchain) NewViaCMake(
 	scriptEarly := attr.ScriptEarly
 	if attr.Writable {
 		scriptEarly = `
-chmod -R +w "${ROSA_CMAKE_SOURCE}"
+chmod -R +w "${ROSA_SOURCE}"
 ` + scriptEarly
 	}
 
@@ -106,6 +106,7 @@ chmod -R +w "${ROSA_CMAKE_SOURCE}"
 		attr.Extra,
 		cmakeExtras,
 	), nil, slices.Concat([]string{
+		"ROSA_SOURCE=" + sourcePath.String(),
 		"ROSA_CMAKE_SOURCE=" + sourcePath.Append(attr.Append...).String(),
 		"ROSA_INSTALL_PREFIX=/work" + prefix.String(),
 	}, attr.Env), scriptEarly+`