Don't bother constructing a Firebird framework and especially don't
pretend we would have it at run-time in
/Library/Frameworks/Firebird.framework. We only need the
libfbembed.dylib, I hope.

We need just libfbembed.dylib, not the version-numbered copies.

Use gb_Helper_set_ld_path instead of manipulating LD_LIBRARY_PATH and
DYLD_LIBRARY_PATH explicitly.

Don't let Firebird's build mechanism totally override DYLD_LIBRARY_PATH.

No need to handle "fb" specially in macosx-change-install-name.pl.

We need to call macosx-change-install-name.pl on libfbembed.dylib,
too.

Change-Id: Id7e6c91a6763e1d5ede5c935b4c4fd946ae00f20