librt: Use -nodefaultlibs instead of -nostdlib

librt: Use -nodefaultlibs instead of -nostdlib

nostdlib disables linking in startup files too which is not
what we want here since it needs to resolve __dso_handle
which comes from crtbeginS.o, otherwise librt has this
undefined reference to a weak undefined __dso_handle that
shows up as error (with gold linker)
when shared libraries are being built which are
linking in librt

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>