CMake: Check whether BSYMBOLIC is supported by the linker.

Linking with '-Bsymbolic-functions' is supported for ELF-binaries, only.

.travis.yml

@@ -128,11 +128,7 @@ before_script:
   - set +e 
   - mkdir -p build || echo "Failed to mkdir build"
   - cd build || echo "Failed to cd build"
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then
-       cmake -DDISABLE_BSYMBOLIC=ON .. ;
-    else 
-       cmake .. ;
-    fi || echo "Failed to run cmake"
+  - cmake .. || echo "Failed to run cmake"
 
 script:
   - make

CMakeLists.txt

@@ -270,7 +270,20 @@ if (NOT ("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC"))
 		add_compile_options("-D_REENTRANT")
 	endif()
 
-	if (DISABLE_BSYMBOLIC STREQUAL "OFF")
+	# OSX Mach-O doesn't support linking with '-Bsymbolic-functions'.
+	# Others may not support it, too.
+	list(APPEND CMAKE_REQUIRED_LIBRARIES "-Wl,-Bsymbolic-functions")
+	check_c_source_compiles(
+	[=[
+	int main ()
+	{
+	  return 0;
+	}
+	]=]
+	BSYMBOLIC_WORKS
+	)
+	list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "-Wl,-Bsymbolic-functions")
+	if (DISABLE_BSYMBOLIC STREQUAL "OFF" AND BSYMBOLIC_WORKS)
 		set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-Bsymbolic-functions")
 		# XXX need cmake>=3.13 for this:
 		#add_link_options("-Wl,-Bsymbolic-functions")