Only the Gb library relies on having undefined references to a
symbol that needs to be provided by the host application. For
all other libraries we can link with -no-undefined.
This actually allows for the user to override the decision and at the
same time supports compilers that might not be able to use -fPIC at
all.
Signed-off-by: Diego Elio Pettenò <flameeyes@flameeyes.eu>