Support for .weak (in addition to the N_INDR stab) for gcc/g++. Also deal

Support for .weak (in addition to the N_INDR stab) for gcc/g++. Also deal
with the -R option and store the path in the dynamic header when specified.
The $LD_RUN_PATH environment variable is not checked yet.

While here, split up the code a bit more to enable more selective replacing
of GPL'ed components that are linked with ld.so with others.

Obtained from: NetBSD (mostly, the breakup is my fault)