[libc++] Remove unneeded visibility pragmas

The function definitions being guarded by the pragma were all static, so
they wouldn't be exported anyway. In any case, we should prefer the
visibility macros. No functional change.

Differential Revision: https://reviews.llvm.org/D26940

llvm-svn: 287768

libcxx/src/chrono.cpp

@@ -90,8 +90,6 @@ steady_clock::now() _NOEXCEPT
 // MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
 //   for that case as an optimization.
 
-#pragma GCC visibility push(hidden)
-
 static
 steady_clock::rep
 steady_simplified()
@@ -129,8 +127,6 @@ init_steady_clock()
     return &steady_full;
 }
 
-#pragma GCC visibility pop
-
 steady_clock::time_point
 steady_clock::now() _NOEXCEPT
 {