Remove check for librt. librt doesn't exist many places anymore and we don't actually use clock_gettime

CMakeLists.txt

@@ -299,16 +299,6 @@ check_type_size("ucontext_t" HAVE_UCONTEXT_T)
 
 # *** LIBRARY CHECKS ***
 
-if(UNIX)
-  include(CheckLibraryExists)
-  CHECK_LIBRARY_EXISTS(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME)
-  if(NOT HAVE_CLOCK_GETTIME)
-    message(FATAL_ERROR "clock_gettime not found")
-  else()
-    list(APPEND ZM_BIN_LIBS "-lrt")
-  endif()
-endif()
-
 # zlib
 find_package(ZLIB)
 if(ZLIB_FOUND)