Do not suppress all Boehm warnings

If something goes wrong during a GC, we likely want to know what
happened.

It's not totally clear whether this is the correct way to disable
warnings anyway (it uses some deprecated library features in Boehm).
Annoying warnings (such as those for many large page allocations) can be
disabled individually.

library/std/src/rt.rs

@@ -103,10 +103,6 @@ unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
         // handler next time. The is not true in the reverse case.
         alloc::gc::init();
 
-        // Boehm GC prints OOM warnings which are useful for debugging, but
-        // annoying when building the compiler in release mode.
-        alloc::gc::suppress_warnings();
-
         sys::init(argc, argv, sigpipe);
 
         let main_guard = sys::thread::guard::init();