[libc] Remove warnings on default values

Summary:
These cause issues because we compile with `-Wno-error`. Remove them for
now. @SchrodingerZhu.

Author: jhuber6

libc/src/__support/threads/linux/raw_mutex.h

@@ -20,7 +20,6 @@
 
 #ifndef LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
 #define LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY 1
-#warning "LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY is not defined, defaulting to 1"
 #endif
 
 #if LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
@@ -29,8 +28,6 @@
 
 #ifndef LIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT
 #define LIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT 100
-#warning                                                                       \
-    "LIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT is not defined, defaulting to 100"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {