libcore: Add core::logging::console_on/off functions

These affect logging output to stdout globally, and turning the console off
has no effect when overridden by RUST_LOG.

src/libcore/core.rc

@@ -10,7 +10,7 @@
 export box, char, float, bessel, f32, f64, int, str, ptr;
 export uint, u8, u32, u64, vec, bool;
 export either, option, result;
-export ctypes, sys, unsafe, comm, task;
+export ctypes, sys, unsafe, comm, task, logging;
 export extfmt;
 export math;
 
@@ -52,6 +52,7 @@ mod sys;
 mod unsafe;
 mod comm;
 mod task;
+mod logging;
 
 // Compiler support modules
 

src/libcore/logging.rs

@@ -0,0 +1,26 @@
+#[doc = "Logging"];
+
+export console_on, console_off;
+
+#[nolink]
+native mod rustrt {
+    fn rust_log_console_on();
+    fn rust_log_console_off();
+}
+
+#[doc = "Turns on logging to stdout globally"]
+fn console_on() {
+    rustrt::rust_log_console_on();
+}
+
+#[doc(
+    brief =
+    "Turns off logging to stdout globally",
+    desc =
+    "Turns off the console unless the user has overridden the \
+     runtime environment's logging spec, e.g. by setting \
+     the RUST_LOG environment variable"
+)]
+fn console_off() {
+    rustrt::rust_log_console_off();
+}