Remove deprecated call to add_compiler_export_flags()

It is deprecated in CMake 3.0, the replacement is to set the
CXX_VISIBILITY_PRESET (or in our case C_VISIBILITY_PRESET) and
VISIBILITY_INLINES_HIDDEN properties of the target.

We're already setting them by setting the CMake variables anyway, so the
call can be removed.

src/CMakeLists.txt

@@ -59,7 +59,6 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/cmark_version.h.in
 include (GenerateExportHeader)
 
 add_executable(${PROGRAM} ${PROGRAM_SOURCES})
-add_compiler_export_flags()
 
 # Disable the PUBLIC declarations when compiling the executable:
 set_target_properties(${PROGRAM} PROPERTIES
@@ -72,12 +71,9 @@ set(CMAKE_LINKER_DEBUG "${CMAKE_LINKER_FLAGS_DEBUG}")
 set(CMAKE_C_FLAGS_PROFILE "${CMAKE_C_FLAGS_RELEASE} -pg")
 set(CMAKE_LINKER_PROFILE "${CMAKE_LINKER_FLAGS_RELEASE} -pg")
 
-if (${CMAKE_VERSION} VERSION_GREATER "1.8")
-  set(CMAKE_C_VISIBILITY_PRESET hidden)
-  set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
-elseif(CMAKE_COMPILER_IS_GNUCC OR ${CMAKE_C_COMPILER_ID} STREQUAL "Clang")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fvisibility=hidden")
-endif ()
+# -fvisibility=hidden
+set(CMAKE_C_VISIBILITY_PRESET hidden)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
 if (CMARK_SHARED)
   add_library(${LIBRARY} SHARED ${LIBRARY_SOURCES})