GNU: Do not use -fvisibility on AIX or HP-UX

Use of `-fvisibility=hidden` warns:

  warning: visibility attribute not supported in this configuration; ignored

Modules/Platform/AIX-GNU-CXX.cmake

@@ -1,2 +1,3 @@
 include(Platform/AIX-GNU)
 __aix_compiler_gnu(CXX)
+unset(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN)

Modules/Platform/AIX-GNU.cmake

@@ -34,4 +34,5 @@ macro(__aix_compiler_gnu lang)
   set(CMAKE_${lang}_USE_IMPLICIT_LINK_DIRECTORIES_IN_RUNTIME_PATH 1)
 
   set(CMAKE_${lang}_LINK_FLAGS "-Wl,-bnoipath")
+  unset(CMAKE_${lang}_COMPILE_OPTIONS_VISIBILITY)
 endmacro()

Modules/Platform/HP-UX-GNU-CXX.cmake

@@ -1,2 +1,3 @@
 include(Platform/HP-UX-GNU)
 __hpux_compiler_gnu(CXX)
+unset(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN)

Modules/Platform/HP-UX-GNU.cmake

@@ -26,4 +26,5 @@ macro(__hpux_compiler_gnu lang)
   set(CMAKE_SHARED_LIBRARY_SONAME_${lang}_FLAG "-Wl,+h")
 
   set(CMAKE_${lang}_LINK_FLAGS "-Wl,+s,+nodefaultrpath")
+  unset(CMAKE_${lang}_COMPILE_OPTIONS_VISIBILITY)
 endmacro()