Only check for pthread library if pthread.h was found.

CMakeLists.txt

@@ -176,11 +176,10 @@ if(UNIX)
         check_include_file(pthread.h HAVE_PTHREAD_H)
         if(HAVE_PTHREAD_H)
             set(PHYSFS_HAVE_THREAD_SUPPORT TRUE)
-        endif()
-
-        find_library(PTHREAD_LIBRARY pthread)
-        if(PTHREAD_LIBRARY)
-            set(OPTIONAL_LIBRARY_LIBS ${OPTIONAL_LIBRARY_LIBS} ${PTHREAD_LIBRARY})
+            find_library(PTHREAD_LIBRARY pthread)
+            if(PTHREAD_LIBRARY)
+                set(OPTIONAL_LIBRARY_LIBS ${OPTIONAL_LIBRARY_LIBS} ${PTHREAD_LIBRARY})
+            endif()
         endif()
     endif()
 endif()