internal/rosa/cmake: pass parallel argument for make

This uses the default value for each build system, which is parallel for ninja but not for make.

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

internal/rosa/cmake.go

@@ -180,8 +180,10 @@ func (attr *CMakeHelper) script(name string) string {
 	}
 
 	generate := "Ninja"
+	jobs := ""
 	if attr.Make {
 		generate = "'Unix Makefiles'"
+		jobs += ` "--parallel=$(nproc)"`
 	}
 
 	return `
@@ -198,7 +200,7 @@ cmake -G ` + generate + ` \
 	}), " \\\n\t") + ` \
 	-DCMAKE_INSTALL_PREFIX=/work/system \
 	'/usr/src/` + name + `/` + path.Join(attr.Append...) + `'
-cmake --build .
+cmake --build .` + jobs + `
 cmake --install .
 ` + attr.Script
 }