Revert "Guard visibility variables on AIX"

This reverts commit d785c299bdb9494182fd253a5ab5e5dbca725a3c.
diff --git a/MicroBenchmarks/libs/benchmark/CMakeLists.txt b/MicroBenchmarks/libs/benchmark/CMakeLists.txt
index 03c0c16..cc80702 100644
--- a/MicroBenchmarks/libs/benchmark/CMakeLists.txt
+++ b/MicroBenchmarks/libs/benchmark/CMakeLists.txt
@@ -51,10 +51,8 @@
 option(BENCHMARK_ENABLE_LIBPFM "Enable performance counters provided by libpfm" OFF)
 
 # Export only public symbols
-if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
-  set(CMAKE_CXX_VISIBILITY_PRESET hidden)
-  set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)
-endif()
+set(CMAKE_CXX_VISIBILITY_PRESET hidden)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)
 
 if(MSVC)
     # As of CMake 3.18, CMAKE_SYSTEM_PROCESSOR is not set properly for MSVC and