Don't link a non-existent pthread library on Android

Author: finagolfin

src/CMakeLists.txt

@@ -162,7 +162,7 @@ if(CMARK_SHARED OR CMARK_STATIC)
   set(CMARK_TARGETS_FILE ${CMAKE_CURRENT_BINARY_DIR}/cmarkTargets.cmake)
   export(TARGETS ${CMARK_INSTALL} FILE ${CMARK_TARGETS_FILE})
 
-  if(CMARK_THREADING AND NOT APPLE AND NOT MSVC)
+  if(CMARK_THREADING AND NOT APPLE AND NOT MSVC AND NOT ANDROID)
     if(CMARK_SHARED)
       target_link_libraries(${LIBRARY} pthread)
     endif(CMARK_SHARED)