cmake: detect linker support

check the linker support of `--version-script` and `--exclude-libs`
flags. and use them only if they are supported.

llvm-ld does not support `--version-script` at this moment. and it's
reported that old versions of llvm-ld do not support `--exclude-libs`
as well.

Signed-off-by: Kefu Chai <kchai@redhat.com>

cmake/modules/CephCheck_link.c

@@ -0,0 +1,2 @@
+int main()
+{}

cmake/modules/CephCheck_link.map

@@ -0,0 +1 @@
+{};

cmake/modules/CephChecks.cmake

@@ -124,3 +124,14 @@ int main(int argc, char **argv)
 else(CMAKE_SYSTEM_PROCESSOR STREQUAL CMAKE_HOST_SYSTEM_PROCESSOR)
   message(STATUS "Assuming unaligned access is supported")
 endif(CMAKE_SYSTEM_PROCESSOR STREQUAL CMAKE_HOST_SYSTEM_PROCESSOR)
+
+# should use LINK_OPTIONS instead of LINK_LIBRARIES, if we can use cmake v3.14+
+try_compile(HAVE_LINK_VERSION_SCRIPT
+  ${CMAKE_CURRENT_BINARY_DIR}
+  SOURCES ${CMAKE_CURRENT_LIST_DIR}/CephCheck_link.c
+  LINK_LIBRARIES "-Wl,--version-script=${CMAKE_CURRENT_LIST_DIR}/CephCheck_link.map")
+
+try_compile(HAVE_LINK_EXCLUDE_LIBS
+  ${CMAKE_CURRENT_BINARY_DIR}
+  SOURCES ${CMAKE_CURRENT_LIST_DIR}/CephCheck_link.c
+  LINK_LIBRARIES "-Wl,--exclude-libs,ALL")

src/librados/CMakeLists.txt

@@ -16,9 +16,11 @@ if(ENABLE_SHARED)
     VERSION 2.0.0
     SOVERSION 2
     VISIBILITY_INLINES_HIDDEN ON)
-  if(NOT APPLE)
+  if(HAVE_LINK_EXCLUDE_LIBS)
     set_property(TARGET librados APPEND_STRING PROPERTY
       LINK_FLAGS " -Wl,--exclude-libs,ALL")
+  endif()
+  if(HAVE_LINK_VERSION_SCRIPT)
     set_property(TARGET librados APPEND_STRING PROPERTY
       LINK_FLAGS " -Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/librados.map")
   endif()