Add a COMPILE_OPTION for a VISIBILITY_INLINES_HIDDEN target property.

This corresponds to the g++ and clang++
option -fvisibility-inlines-hidden on linux. On Windows with MinGW,
this corresponds to -fno-keep-inline-dllexport. That option is
not supported by clang currently.

Modules/Compiler/Clang-CXX.cmake

@@ -1,2 +1,4 @@
 include(Compiler/Clang)
 __compiler_clang(CXX)
+
+set(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN "-fvisibility-inlines-hidden")

Modules/Compiler/GNU-CXX.cmake

@@ -1,2 +1,12 @@
 include(Compiler/GNU)
 __compiler_gnu(CXX)
+
+if (WIN32)
+  if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.6)
+    set(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN "-fno-keep-inline-dllexport")
+  endif()
+else()
+  if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.2)
+    set(CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY_INLINES_HIDDEN "-fvisibility-inlines-hidden")
+  endif()
+endif()