Add FreeBSD defined to CMakeLists.txt

- Detect FreeBSD.
- Set both PLATFORM_UNIX and PLATFORM_FREEBSD. The latter is required to
  distinguish FreeBSD from other unixoid platforms like Linux.
- On FreeBSD 3rd party libs are installed to /usr/local, we need to add
  /usr/local/include as include directory.
- Add linker options for FreeBSD. FreeBSD has no -ldl.

Sources/CMakeLists.txt

@@ -28,6 +28,9 @@ endif()
 if(CMAKE_SYSTEM_NAME STREQUAL "Linux" OR CMAKE_SYSTEM_NAME MATCHES "GNU|kFreeBSD")
     SET(LINUX TRUE)
 endif()
+if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
+    SET(FREEBSD TRUE)
+endif()
 if(APPLE)
     SET(MACOSX TRUE)
 endif()
@@ -71,6 +74,16 @@ if(LINUX)
     add_definitions(-DPRAGMA_ONCE=1)
 endif()
 
+if(FREEBSD)
+    set(CMAKE_SKIP_RPATH ON CACHE BOOL "Skip RPATH" FORCE)
+    add_definitions(-DPLATFORM_UNIX=1)
+    add_definitions(-DPLATFORM_FREEBSD=1)
+    add_definitions(-D_FILE_OFFSET_BITS=64)
+    add_definitions(-D_LARGEFILE_SOURCE=1)
+    add_definitions(-DPRAGMA_ONCE=1)
+    include_directories("/usr/local/include")
+endif()
+
 if(MACOSX)
     add_definitions(-DPLATFORM_UNIX=1)
     add_definitions(-DPLATFORM_MACOSX=1)
@@ -826,6 +839,19 @@ if(LINUX)
     endif()
 endif()
 
+if(FREEBSD)
+    set_target_properties(ssam PROPERTIES LINK_FLAGS "-Wl,-rpath,$ORIGIN")
+    target_link_libraries(ssam "m")
+    target_link_libraries(ssam "pthread")
+    target_link_libraries(ssam ${SDL2_LIBRARY})
+    if(BUILD_DEDICATED_SERVER)
+        set_target_properties(SeriousSamDedicated PROPERTIES LINK_FLAGS "-Wl,-rpath,$ORIGIN")
+        target_link_libraries(SeriousSamDedicated "m")
+        target_link_libraries(SeriousSamDedicated "pthread")
+        target_link_libraries(SeriousSamDedicated ${SDL2_LIBRARY})
+    endif()
+endif()
+
 if(TFE)
  set_target_properties(ssam PROPERTIES OUTPUT_NAME "ssam-tfe")
 endif()