message: build: remove linking librt for backwards compatibility
  The clock_* functions from librt were merged into glibc as part of the
  2.17 release, so this is no longer needed.
diff: @@ -659,11 +659,6 @@ AX_GCC_FUNC_ATTRIBUTE([dllexport])
  AX_GCC_FUNC_ATTRIBUTE([dllimport])
  if test x$use_glibc_compat != xno; then
  -
  - #glibc absorbed clock_gettime in 2.17. librt (its previous location) is safe to link
  - #in anyway for back-compat.
  - AC_CHECK_LIB([rt],[clock_gettime],, AC_MSG_ERROR(librt missing))
  -
  AX_CHECK_LINK_FLAG([[-Wl,--wrap=__divmoddi4]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=__divmoddi4"])
  AX_CHECK_LINK_FLAG([[-Wl,--wrap=log2f]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=log2f"])
  else
  